Toward 1D Transport in 3D Materials: SOC-Induced Charge-Transport Anisotropy in Sm3ZrBi5.

1D charge transport offers great insight into strongly correlated physics, such as Luttinger liquids, electronic instabilities, and superconductivity. Although 1D charge transport is observed in nanomaterials and quantum wires, examples in bulk crystalline solids remain elusive. In this work, it is demonstrated that spin-orbit coupling (SOC) can act as a mechanism to induce quasi-1D charge transport in the Ln3MPn5 (Ln = lanthanide; M = transition metal; Pn = Pnictide) family. From three example compounds, La3ZrSb5, La3ZrBi5, and Sm3ZrBi5, density functional theory calculations with SOC included show a quasi-1D Fermi surface in the bismuthide compounds, but an anisotropic 3D Fermi surface in the antimonide structure. By performing anisotropic charge transport measurements on La3ZrSb5, La3ZrBi5, and Sm3ZrBi5, it is demonstrated that SOC starkly affects their anisotropic resistivity ratios (ARR) at low temperatures, with an ARR of ≈4 in the antimonide compared to ≈9.5 and ≈22 (≈32 after magnetic ordering) in La3ZrBi5 and Sm3ZrBi5, respectively. This report demonstrates the utility of spin-orbit coupling to induce quasi-low-dimensional Fermi surfaces in anisotropic crystal structures, and provides a template for examining other systems.

Chemical Bonding Induces One-Dimensional Physics in Bulk Crystal BiIr4Se8.

One-dimensional (1D) systems persist as some of the most interesting because of the rich physics that emerges from constrained degrees of freedom. A desirable route to harness the properties therein is to grow bulk single crystals of a physically three-dimensional (3D) but electronically 1D compound. Most bulk compounds which approach the electronic 1D limit still field interactions across the other two crystallographic directions and, consequently, deviate from the 1D models. In this paper, we lay out chemical concepts to realize the physics of 1D models in 3D crystals. These are based on both structural and electronic arguments. We present BiIr4Se8, a bulk crystal consisting of linear Bi2+ chains within a scaffolding of IrSe6 octahedra, as a prime example. Through crystal structure analysis, density functional theory calculations, X-ray diffraction, and physical property measurements, we demonstrate the unique 1D electronic configuration in BiIr4Se8. This configuration at ambient temperature is a gapped Su-Schriefer-Heeger system, generated by way of a canonical Peierls distortion involving Bi dimerization that relieves instabilities in a 1D metallic state. At 190 K, an additional 1D charge density wave distortion emerges, which affects the Peierls distortion. The experimental evidence validates our design principles and distinguishes BiIr4Se8 among other quasi-1D bulk compounds. We thus show that it is possible to realize unique electronically 1D materials applying chemical concepts.

Chemical exfoliation of 1-dimensional antiferromagnetic nanoribbons from a non-van der Waals material.

As the demand for increasingly varied types of 1-dimensional (1D) materials grows, there is a greater need for new methods to synthesize these types of materials in a simple and scalable way. Chemical exfoliation is commonly used to make 2-dimensional (2D) materials, often in a way that is both straightforward and suitable for making larger quantities, yet this method has thus far been underutilized for synthesizing 1D materials. In the few instances when chemical exfoliation has been used to make 1D materials, the starting compound has been a van der Waals material, thus excluding any structures without these weak bonds inherently present. We demonstrate here that ionically bonded crystals can also be chemically exfoliated to 1D structures by choosing KFeS2 as an example. Using chemical exfoliation, antiferromagnetic 1D nanoribbons can be yielded in a single step. The nanoribbons are crystalline and closely resemble the parent compound both in structure and in intrinsic antiferromagnetism. The facile chemical exfoliation of an ionically bonded crystal shown in this work opens up opportunities for the synthesis of both magnetic and non-magnetic 1D nanomaterials from a greater variety of starting structures.

Evidence for two dimensional anisotropic Luttinger liquids at millikelvin temperatures.

Interacting electrons in one dimension (1D) are governed by the Luttinger liquid (LL) theory in which excitations are fractionalized. Can a LL-like state emerge in a 2D system as a stable zero-temperature phase? This question is crucial in the study of non-Fermi liquids. A recent experiment identified twisted bilayer tungsten ditelluride (tWTe2) as a 2D host of LL-like physics at a few kelvins. Here we report evidence for a 2D anisotropic LL state down to 50 mK, spontaneously formed in tWTe2 with a twist angle of ~ 3o. While the system is metallic-like and nearly isotropic above 2 K, a dramatically enhanced electronic anisotropy develops in the millikelvin regime. In the anisotropic phase, we observe characteristics of a 2D LL phase including a power-law across-wire conductance and a zero-bias dip in the along-wire differential resistance. Our results represent a step forward in the search for stable LL physics beyond 1D.

A platform for far-infrared spectroscopy of quantum materials at millikelvin temperatures.

Optical spectroscopy of quantum materials at ultralow temperatures is rarely explored, yet it may provide critical characterizations of quantum phases not possible using other approaches. We describe the development of a novel experimental platform that enables optical spectroscopic studies, together with standard electronic transport, of materials at millikelvin temperatures inside a dilution refrigerator. The instrument is capable of measuring both bulk crystals and micrometer-sized two-dimensional van der Waals materials and devices. We demonstrate its performance by implementing photocurrent-based Fourier transform infrared spectroscopy on a monolayer WTe2 device and a multilayer 1T-TaS2 crystal, with a spectral range available from the near-infrared to the terahertz regime and in magnetic fields up to 5 T. In the far-infrared regime, we achieve spectroscopic measurements at a base temperature as low as ∼43 mK and a sample electron temperature of ∼450 mK. Possible experiments and potential future upgrades of this versatile instrumental platform are envisioned.

Colossal magnetoresistance in the multiple wave vector charge density wave regime of an antiferromagnetic Dirac semimetal.

Colossal negative magnetoresistance is a well-known phenomenon, notably observed in hole-doped ferromagnetic manganites. It remains a major research topic due to its potential in technological applications. In contrast, topological semimetals show large but positive magnetoresistance, originated from the high-mobility charge carriers. Here, we show that in the highly electron-doped region, the Dirac semimetal CeSbTe demonstrates similar properties as the manganites. CeSb0.11Te1.90 hosts multiple charge density wave modulation vectors and has a complex magnetic phase diagram. We confirm that this compound is an antiferromagnetic Dirac semimetal. Despite having a metallic Fermi surface, the electronic transport properties are semiconductor-like and deviate from known theoretical models. An external magnetic field induces a semiconductor metal-like transition, which results in a colossal negative magnetoresistance. Moreover, signatures of the coupling between the charge density wave and a spin modulation are observed in resistivity. This spin modulation also produces a giant anomalous Hall response.

Atomic Resolution Imaging of Highly Air-Sensitive Monolayer and Twisted-Bilayer WTe2.

Bulk Td-WTe2 is a semimetal, while its monolayer counterpart is a two-dimensional (2D) topological insulator. Recently, electronic transport resembling a Luttinger liquid state was found in twisted-bilayer WTe2 (tWTe2) with a twist angle of ∼5°. Despite the strong interest in 2D WTe2 systems, little experimental information is available about their intrinsic microstructure, leaving obstacles in modeling their physical properties. The monolayer, and consequently tWTe2, are highly air-sensitive, and therefore, probing their atomic structures is difficult. In this study, we develop a robust method for atomic-resolution visualization of monolayers and tWTe2 obtained through mechanical exfoliation and fabrication. We confirm the high crystalline quality of mechanically exfoliated WTe2 samples and observe that tWTe2 with twist angles of ∼5 and ∼2° retains its pristine moiré structure without substantial deformations or reconstructions. The results provide a structural foundation for future electronic modeling of monolayer and tWTe2 moiré lattices.

Anisotropic transport properties and high-mobility of charge carriers of antiferromagnetic GdAgSb2.

We report detailed magnetic and magnetotransport properties of single-crystalline GdAgSb2antiferromagnet. The electronic transport properties show metallic behavior along with large, anisotropic, and non-saturating magnetoresistance (MR) in transverse experimental configuration. At 2 K and 9 T, the value of MR reaches as high as ∼1.8×103%. The anisotropic MR along with additional features for applied magnetic field along some specific crystallographic directions reveal the quasi-two-dimensional nature of the Fermi surface of GdAgSb2. Hall resistivity confirms the presence of two types of charge carriers. The high carrier mobilities (∼1.2×104 cm2 V-1 s-1) and nearly-compensated electron and hole-density (∼1019 cm-3) could be responsible for the large transverse MR in GdAgSb2. We have also observed the de Haas-van Alphen oscillations in the magnetization measurements below 7 K. Furthermore, the robust planar Hall effect, which persists up to high temperatures, could indicate the nontrivial nature of the electronic band structure for GdAgSb2.

Synthesis of an aqueous, air-stable, superconducting 1T'-WS2 monolayer ink.

Liquid-phase chemical exfoliation can achieve industry-scale production of two-dimensional (2D) materials for a wide range of applications. However, many 2D materials with potential applications in quantum technologies often fail to leave the laboratory setting because of their air sensitivity and depreciation of physical performance after chemical processing. We report a simple chemical exfoliation method to create a stable, aqueous, surfactant-free, superconducting ink containing phase-pure 1T'-WS2 monolayers that are isostructural to the air-sensitive topological insulator 1T'-WTe2. The printed film is metallic at room temperature and superconducting below 7.3 kelvin, shows strong anisotropic unconventional superconducting behavior with an in-plane and out-of-plane upper critical magnetic field of 30.1 and 5.3 tesla, and is stable at ambient conditions for at least 30 days. Our results show that chemical processing can make nontrivial 2D materials that were formerly only studied in laboratories commercially accessible.

Chemical Exfoliation toward Magnetic 2D VOCl Monolayers.

The diversification of magnetic two-dimensional (2D) materials holds the key to the further development of advanced technologies, such as spintronic devices and efficient data storage. However, the search for intrinsic magnetism down to the 2D limit is severely limited by the ability to reliably exfoliate large, air-stable nanosheets. Chemical exfoliation, a relatively underutilized method for delamination, offers many advantages, including a high degree of adaptability and higher yields of uniformly exfoliated materials. van der Waals (vdW) materials, in particular the family of transition-metal oxyhalides, are ideal candidates for chemical exfoliation due to their large interlayer spacing and the wide variety of interesting magnetic properties they exhibit. In this study, we employ a chemical exfoliation method to delaminate the layered antiferromagnet vanadium oxychloride (VOCl) down to the monolayer limit. The resulting nansoheets have lateral sizes of up to 20 µm, are air-stable, and can be easily isolated. Magnetic characterization was performed throughout the exfoliation process, tracking the changes in magnetic behavior among bulk VOCl, its lithiated intercalate, and the restacked nanosheet pellet. The results from this work demonstrate the potential of chemical exfoliation, along with illustrating the effects of low dimensionality on magnetic properties.

One-dimensional Luttinger liquids in a two-dimensional moiré lattice.

The Luttinger liquid (LL) model of one-dimensional (1D) electronic systems provides a powerful tool for understanding strongly correlated physics, including phenomena such as spin-charge separation1. Substantial theoretical efforts have attempted to extend the LL phenomenology to two dimensions, especially in models of closely packed arrays of 1D quantum wires2-13, each being described as a LL. Such coupled-wire models have been successfully used to construct two-dimensional (2D) anisotropic non-Fermi liquids2-6, quantum Hall states7-9, topological phases10,11 and quantum spin liquids12,13. However, an experimental demonstration of high-quality arrays of 1D LLs suitable for realizing these models remains absent. Here we report the experimental realization of 2D arrays of 1D LLs with crystalline quality in a moiré superlattice made of twisted bilayer tungsten ditelluride (tWTe2). Originating from the anisotropic lattice of the monolayer, the moiré pattern of tWTe2 hosts identical, parallel 1D electronic channels, separated by a fixed nanoscale distance, which is tuneable by the interlayer twist angle. At a twist angle of approximately 5 degrees, we find that hole-doped tWTe2 exhibits exceptionally large transport anisotropy with a resistance ratio of around 1,000 between two orthogonal in-plane directions. The across-wire conductance exhibits power-law scaling behaviours, consistent with the formation of a 2D anisotropic phase that resembles an array of LLs. Our results open the door for realizing a variety of correlated and topological quantum phases based on coupled-wire models and LL physics.

A Class of Magnetic Topological Material Candidates with Hypervalent Bi Chains.

The link between crystal and electronic structure is crucial for understanding structure-property relations in solid-state chemistry. In particular, it has been instrumental in understanding topological materials, where electrons behave differently than they would in conventional solids. Herein, we identify 1D Bi chains as a structural motif of interest for topological materials. We focus on Sm3ZrBi5, a new quasi-one-dimensional (1D) compound in the Ln3MPn5 (Ln = lanthanide; M = metal; Pn = pnictide) family that crystallizes in the P63/mcm space group. Density functional theory calculations indicate a complex, topologically nontrivial electronic structure that changes significantly in the presence of spin-orbit coupling. Magnetic measurements show a quasi-1D antiferromagnetic structure with two magnetic transitions at 11.7 and 10.7 K that are invariant to applied field up to 9 T, indicating magnetically frustrated spins. Heat capacity, electrical, and thermoelectric measurements support this claim and suggest complex scattering behavior in Sm3ZrBi5. This work highlights 1D chains as an unexplored structural motif for identifying topological materials, as well as the potential for rich physical phenomena in the Ln3MPn5 family.

Effect of Co and Mg doping at Cu site on structural, magnetic and dielectric properties of α-Cu2V2O7.

We have studied the effect of doping of both magnetic (Co) and nonmagnetic (Mg) ions at the Cu site on phase transition in polycrystalline α-Cu2V2O7through structural, magnetic, and electrical measurements. X-ray diffraction reveals that Mg doping triggers an onset ofα- toß-phase structural transition in Cu2-xMgxV2O7above a critical Mg concentrationxc= 0.15, and both the phases coexist up tox= 0.25. Cu2V2O7possesses a non-centrosymmetric crystal structure and antiferromagnetic ordering along with a non-collinear spin structure in theαphase, originated from the microscopic Dzyaloshinskii-Moriya interaction between the neighboring Cu spins. Accordingly, a weak ferromagnetic (FM) behavior has been observed up tox= 0.25. However, beyond this concentration, Cu2-xMgxV2O7exhibits complex magnetic properties. A clear dielectric anomaly is observed in α-Cu2-xMgxV2O7around the magnetic transition temperature, which loses its prominence with the increase in Mg doping. The analysis of experimental data shows that the magnetoelectric coupling is nonlinear, which is in agreement with the Landau theory of continuous phase transitions. Co doping, on the other hand, initiates a sharpαtoßphase transition around the same critical concentrationxc= 0.15 in Cu2-xCoxV2O7but the FM behavior is very weak and can be detected only up tox= 0.10. We have drawn the magnetic phase diagram which indicates that the rate of suppression in transition temperature is the same for both types of doping, magnetic (Co) and nonmagnetic (Zn/Mg).

Evolving Devil's Staircase Magnetization from Tunable Charge Density Waves in Nonsymmorphic Dirac Semimetals.

While several magnetic topological semimetals have been discovered in recent years, their band structures are far from ideal, often obscured by trivial bands at the Fermi energy. Square-net materials with clean, linearly dispersing bands show potential to circumvent this issue. CeSbTe, a square-net material, features multiple magnetic-field-controllable topological phases. Here, it is shown that in this material, even higher degrees of tunability can be achieved by changing the electron count at the square-net motif. Increased electron filling results in structural distortion and formation of charge density waves (CDWs). The modulation wave-vector evolves continuously leading to a region of multiple discrete CDWs and a corresponding complex "Devil's staircase" magnetic ground state. A series of fractionally quantized magnetization plateaus is observed, which implies direct coupling between CDW and a collective spin-excitation. It is further shown that the CDW creates a robust idealized nonsymmorphic Dirac semimetal, thus providing access to topological systems with rich magnetism.

Tip-induced superconductivity coexisting with preserved topological properties in line-nodal semimetal ZrSiS.

ZrSiS was recently shown to be a new material with topologically non-trivial band structure that exhibits multiple Dirac nodes and a robust linear band dispersion up to an unusually high energy of 2 eV. Such a robust linear dispersion makes the topological properties of ZrSiS insensitive to perturbations like carrier doping or lattice distortion. Here, we show that a novel superconducting phase with a remarkably high [Formula: see text] of 7.5 K can be induced in single crystals of ZrSiS by a non-superconducting metallic tip of Ag. From first-principles calculations, we show that the observed superconducting phase might originate from a dramatic enhancement of density of states due to the presence of a metallic tip on ZrSiS. Our calculations also show that the emerging tip-induced superconducting phase co-exists with the well preserved topological properties of ZrSiS.

Anisotropic transverse magnetoresistance and Fermi surface in TaSb2.

TaSb2 has been predicted theoretically to be a weak topological insulator. Whereas, the earlier magnetotransport experiment has established it as a topological semimetal. In the previous works, the Shubnikov-de Haas oscillation has been analyzed to probe the Fermi surface, with magnetic field along a particular crystallographic axis only. By employing a sample rotator, we reveal highly anisotropic transverse magnetoresistance by rotating the magnetic field along different crystallographic directions. To probe the anisotropy in the Fermi surface, we have performed magnetization measurements and detected strong de Haas-van Alphen (dHvA) oscillations for the magnetic field applied along a and b axes as well as perpendicular to ab plane of the crystals. Three Fermi pockets have been identified by analyzing the dHvA oscillations. With the application of magnetic field along different crystal directions, the cross-sectional areas of the Fermi pockets have been found significantly different, i.e., the Fermi pockets are highly anisotropic in nature. Three-band fitting of electrical and Hall conductivity reveals two high mobility electron pockets and one low mobility hole pocket. The angular variation of transverse magnetoresistance has been qualitatively explained using the results of dHvA oscillations and three-band analysis.

Fermi surface topology and signature of surface Dirac nodes in LaBi.

Novel topological state of matter is one of the rapidly growing fields in condensed matter physics research in recent times. While these materials are fascinating from the aspect of fundamental physics of relativistic particles, their exotic transport properties are equally compelling due to the potential technological applications. Extreme magnetoresistance and ultrahigh carrier mobility are two such major hallmarks of topological materials and often used as primary criteria for identifying new compounds belonging to this class. Recently, LaBi has emerged as a new system, which exhibits the above mentioned properties. However, the topological nature of its band structure remains unresolved. Here, using the magnetotransport and magnetization measurements, we have probed the bulk and surface states of LaBi. Similar to earlier reports, extremely large magnetoresistance and high carrier mobility have been observed with compensated electron and hole density. The Fermi surface properties have been analyzed from both Shubnikov-de Haas and de Haas-van Alphen oscillation techniques. In the magnetization measurement, a prominent paramagnetic singularity has been observed, which demonstrates the non-trivial nature of the surface states in LaBi. Our study unambiguously confirms that LaBi is a three-dimensional topological insulator with possible linear dispersion in the gapped bulk band structure.

Large nonsaturating magnetoresistance and signature of nondegenerate Dirac nodes in ZrSiS.

Whereas the discovery of Dirac- and Weyl-type excitations in electronic systems is a major breakthrough in recent condensed matter physics, finding appropriate materials for fundamental physics and technological applications is an experimental challenge. In all of the reported materials, linear dispersion survives only up to a few hundred millielectronvolts from the Dirac or Weyl nodes. On the other hand, real materials are subject to uncontrolled doping during preparation and thermal effect near room temperature can hinder the rich physics. In ZrSiS, angle-resolved photoemission spectroscopy measurements have shown an unusually robust linear dispersion (up to [Formula: see text]2 eV) with multiple nondegenerate Dirac nodes. In this context, we present the magnetotransport study on ZrSiS crystal, which represents a large family of materials (WHM with W = Zr, Hf; H = Si, Ge, Sn; M = O, S, Se, Te) with identical band topology. Along with extremely large and nonsaturating magnetoresistance (MR), [Formula: see text]1.4 [Formula: see text] 105% at 2 K and 9 T, it shows strong anisotropy, depending on the direction of the magnetic field. Quantum oscillation and Hall effect measurements have revealed large hole and small electron Fermi pockets. A nontrivial [Formula: see text] Berry phase confirms the Dirac fermionic nature for both types of charge carriers. The long-sought relativistic phenomenon of massless Dirac fermions, known as the Adler-Bell-Jackiw chiral anomaly, has also been observed.