Spin polarization in quantum point contact based on wurtzite topological quantum well.

Manipulating spin polarization in wide-gap wurtzite semiconductors is crucial for the development of high-temperature spintronics applications. A topological insulator revealed recently in wurtzite quantum wells (QWs) provides a platform to mediate spin-polarized transport through the polarization field-driven topological edges and large Rashba spin-orbit coupling (SOC). Here, we propose a spin-polarized device in a quantum point contact (QPC) structure based on ZnO/CdO wurtzite topological QWs. The results show that the QPC width can sufficiently control the lateral spin-orbit coupling (SOC) as well as the band gap of the edge states through the quantum size effect. As a result, the spin-polarized conductance exhibits oscillation due to the spin precession, which can be controlled by adjusting the voltage imposed on the split gate. The QPC-induced large spin splitting is highly nonlinear and becomes strong close to the gap. The spin splitting of the edge states will be suppressed for QPC widths greater than 50 nm, and thus lead to an extremely long spin precession length. This QPC width-dependent lateral SOC effect provides an emerging electrical approach to manipulate spin-polarized electron transport in topological wurtzite systems.

Piezoelectric manipulation of spin-orbit coupling in a Wurtzite heterostructure.

The combination of piezoelectricity and spin-orbit coupling (SOC) effect makes wurtzite semiconductors attractive for the development of exotic spin-related physics as well as spintronic applications. Triggering piezoelectricity, particularly by an external stimulus, provides a new perspective for manipulating SOC, but until now, a comprehensive understanding of this mechanism is lacking. Herein, by means of self-consistent calculations and Löwdin perturbation approach, we have explored the manipulation of SOC in the wurtzite (Al, Ga)N/GaN heterostructure by external stress-induced piezoelectric polarization. The results suggest that the Rashba SOC depends weakly on stress due to the wide-gap feature of the wurtzite crystal that makes Rashba SOC predominant by a bulk term instead of the structural inversion term. The piezoelectric polarization diminishes and even turns off Dresselhaus coupling by reducing the interfacial electric field. Moreover, piezoelectricity is shown to improve the poorly gate-tunable SOC. In the heterostructure with two occupied subbands, the Dresselhaus coupling of the second subband is more sensitive than the first one in response to stress. As an extension, we further demonstrate that the correlation effect in the wurtzite heterostructure can be significantly enhanced by piezoelectric polarization. This study offers an in-depth insight into piezoelectric modulation of spin-orbit physics, which has the potential for stimulating new quantum correlation states or designing functional spintronic devices.

Facile Vertical Structure Broadband Photodetectors Enabled by Polyvinylpyrrolidone-Regulated Perovskite and Near-Infrared-Sensitive Lead Phthalocyanine.

Broadband photodetectors have drawn tremendous attention in many application areas such as imaging, optical communication, and biochemical sensing. Perovskite is a star material with broad spectral absorption, but it is challenging to develop ultraviolet-visible-near-infrared (UV-Vis-NIR) ultra-broadband photodetectors due to the insufficient absorption in the near-infrared region. Moreover, it is difficult to construct a diode-type photodetector with a simple vertical structure based only on perovskite materials. Here, facile vertical structure broadband photodetectors were fabricated based on heterojunctions that were composed of perovskite MAPbI3 films with UV-Vis absorption spectrum and small organic molecule lead phthalocyanine (PbPc) with strong NIR optical absorption, resulting in UV-Vis-NIR ultra-broadband photodetection. The quality of MAPbI3 films was improved by introducing polyvinylpyrrolidone (PVP) modification, and subsequently, the corresponding MAPbI3/PbPc heterojunction-based photodetectors exhibited rectification characteristics and reduced reverse dark currents. When the PVP mass ratio is 1 wt%, the photodetector achieved the best performance that the spectral response uniformity factor was as high as 0.77, the photoresponsivity exceeded 10 A/W, and the photoresponse time was less than 0.5 ms under a light intensity of 0.013 mW/cm2 in the UV-Vis to NIR spectral range. These results are comparable or superior to those of some inorganic, organic, and perovskite photodetectors reported previously. This study would provide an effective strategy to construct high-performance perovskite photodetectors based on a simple vertical structure, paving the way to the realization of UV-Vis-NIR broadband photodetection.

Long Tunneled External Ventricular Drains with Shunt Valves: A Technical Note.

BACKGROUND: External ventricular drain (EVD) is a basic operation in neurosurgery. Due to the limitation of its safe duration, some patients need to receive multiple drainage operations. We describe the long tunneled EVD (LTEVD) with shunt valves that effectively avoid multiple operations as a technical note. METHODS: The difference is that the middle part of the drainage tube is connected by an externalized shunt valve. The drainage tube is buried under the skin and the outlet is in the abdomen. The technique and more details are described. RESULTS: The connection between the LTEVD and the shunt valve is simple and the required materials are easily accessible. Externalized valves allow the cerebrospinal fluid to be visualized and more controllable, making it easier for physicians to manage the cerebrospinal fluid. No drainage tube failure or secondary infection was observed. The indwelling time of the drainage tube was greatly extended. CONCLUSIONS: LTEVD is effective and simple. It allows visual control of drainage flow, prolonging catheter indwelling time and eliminating the need for multiple surgeries.

A Keyhole Approach Centered by Anterior Squamous Suture to Hypertensive Basal Ganglia Hemorrhage.

OBJECTIVE: This study aimed to improve the accuracy and efficacy of the keyhole transsylvian approach to remove hypertensive basal ganglia hemorrhage. The authors presented a stable keyhole craniotomy based on anterior squamous suture to expose insular cortex and basal ganglia. METHODS: Twenty-nine patients with hypertensive basal ganglia hemorrhage were treated with keyhole surgery and studied in Guangdong sanjiu brain hospital. RESULTS: By using a bone suture marked keyhole transsylvian approach, near-complete (90%) hematoma evacuation was achieved in 21 cases (72.4), 70% to 90% in 8 cases (24.1), and less than 70% in 1 case (3.4%). In our cohort, 55.1% (16/29) with good function (GOS score 4-5), 41.3% (12/29) with disability (GOS score 3), and 3.4% (1/29) in a vegetative state (GOS score 2). No patients died within 6 months of operation. CONCLUSIONS: Our method can greatly minimize the bone exposure and precisely located the distal Sylvian fissure. A stable keyhole craniotomy based on bone suture can be identically safe and effective in comparison with classic surgery, and it consumes less time and less intra-operative bleeding.

Outcome of Epidural Hematoma: Lessons from Solitary Fibrous Tumor/Hemangiopericytoma.

BACKGROUND: Intracranial solitary fibrous tumor (SFT)/hemangiopericytoma (HPC) is rare. In this report, a case of epidural hematoma (EDH) that eventually evolved into SFT/HPC is presented. We describe the possible association between the 2 diseases, which has not been previously reported. CASE DESCRIPTION: A 40-year-old man suffered from an EDH in the right parietal area 12 years ago and accepted conservative treatment. Follow-up computed tomography (CT) scan shows that the density of the right EDH gradually changed from uniform slightly lower density to mixed density. A new CT scan revealed an epidural mass extending to the subcutaneous with local bone destruction. An operation was performed via a large right parietal craniotomy, and the final diagnosis was World Health Organization grade III SFT/HPC after histopathologic examination and immunohistochemical verification. The patient died of deterioration of brain disease 3 months after the final diagnosis. CONCLUSIONS: To our knowledge, this is the first report that HPC occurred in the epidural cavity. We are the first time to describe the possible association between EDH and HPC.

Bronchogenic Cyst: Skull Base Lesions with Extracranial Extension.

BACKGROUND: Intracranial bronchogenic cysts (BCs) are extremely rare. To our knowledge, this is the first report of a BC in which lesions involve the middle and posterior cranial fossa, as well as the infratemporal fossa. CASE DESCRIPTION: We present the case of a 38-year-old woman who suffered from a cranial nerve dysfunction for 2 years. Magnetic resonance imaging showed that there were skull base communication lesions across the middle and posterior fossa. The patient was operated on through an infratemporal fossa approach. The final diagnosis was BC after histopathologic examination and immunohistochemical verification. The patient's neurologic dysfunction was partially ameliorated at the half-year follow-up. CONCLUSIONS: Intracranial BCs are rare. However, they should be considered in the differential diagnosis for cystic lesions with edge enhancement or extracranial extension.