Novel Strongly Spin-Orbit Coupled Quantum Dimer Magnet: Yb_{2}Si_{2}O_{7}.

The quantum dimer magnet (QDM) is the canonical example of quantum magnetism. The QDM state consists of entangled nearest-neighbor spin dimers and often exhibits a field-induced triplon Bose-Einstein condensate (BEC) phase. We report on a new QDM in the strongly spin-orbit coupled, distorted honeycomb-lattice material Yb_{2}Si_{2}O_{7}. Our single crystal neutron scattering, specific heat, and ultrasound velocity measurements reveal a gapped singlet ground state at zero field with sharp, dispersive excitations. We find a field-induced magnetically ordered phase reminiscent of a BEC phase, with exceptionally low critical fields of H_{c1}∼0.4 and H_{c2}∼1.4 T. Using inelastic neutron scattering in an applied magnetic field we observe a Goldstone mode (gapless to within δE=0.037 meV) that persists throughout the entire field-induced magnetically ordered phase, suggestive of the spontaneous breaking of U(1) symmetry expected for a triplon BEC. However, in contrast to other well-known cases of this phase, the high-field (µ_{0}H≥1.2 T) part of the phase diagram in Yb_{2}Si_{2}O_{7} is interrupted by an unusual regime signaled by a change in the field dependence of the ultrasound velocity and magnetization, as well as the disappearance of a sharp anomaly in the specific heat. These measurements raise the question of how anisotropy in strongly spin-orbit coupled materials modifies the field induced phases of QDMs.

Tunable Quantum Spin Liquidity in the 1/6th-Filled Breathing Kagome Lattice.

We present measurements on a series of materials, Li_{2}In_{1-x}Sc_{x}Mo_{3}O_{8}, that can be described as a 1/6th-filled breathing kagome lattice. Substituting Sc for In generates chemical pressure which alters the breathing parameter nonmonotonically. Muon spin rotation experiments show that this chemical pressure tunes the system from antiferromagnetic long range order to a quantum spin liquid phase. A strong correlation with the breathing parameter implies that it is the dominant parameter controlling the level of magnetic frustration, with increased kagome symmetry generating the quantum spin liquid phase. Magnetic susceptibility measurements suggest that this is related to distinct types of charge order induced by changes in lattice symmetry, in line with the theory of Chen et al. [Phys. Rev. B 93, 245134 (2016)PRBMDO2469-995010.1103/PhysRevB.93.245134]. The specific heat for samples at intermediate Sc concentration, which have the minimum breathing parameter, show consistency with the predicted U(1) quantum spin liquid.

Singlet ground state of the quantum antiferromagnet Ba(3)CuSb(2)O(9).

We present local probe results on the honeycomb lattice antiferromagnet Ba(3)CuSb(2)O(9). Muon spin relaxation measurements in a zero field down to 20 mK show unequivocally that there is a total absence of spin freezing in the ground state. Sb NMR measurements allow us to track the intrinsic susceptibility of the lattice, which shows a maximum at around 55 K and drops to zero in the low-temperature limit. The spin-lattice relaxation rate shows two characteristic energy scales, including a field-dependent crossover to exponential low-temperature behavior, implying gapped magnetic excitations.

Evidence of spin glass dynamics in dilute LiHoxY1-xF4.

ac susceptibility measurements are presented on the dilute, dipolar coupled, Ising magnet LiHoxY1-xF4 for a concentration x=0.045. The frequency and temperature dependences of the susceptibility show characteristic glassy relaxation. The absorption spectrum is found to broaden with decreasing temperature suggesting that the material is behaving as a spin glass and not as an exotic spin liquid as was previously observed. A dynamical scaling analysis suggests a spin glass transition temperature of 43+/-2 mK with an exponent znu=7.8+/-0.2.

Evidence for gapped spin-wave excitations in the frustrated Gd2Sn2O7 pyrochlore antiferromagnet from low-temperature specific heat measurements.

We have measured the low-temperature specific heat of the geometrically frustrated pyrochlore Heisenberg antiferromagnet Gd2Sn2O7 in zero magnetic field. The specific heat is found to drop exponentially below approximately 350 mK. This provides evidence for a gapped spin-wave spectrum due to an anisotropy resulting from single-ion effects and long-range dipolar interactions. The data are well fitted by linear spin-wave theory, ruling out unconventional low-energy magnetic excitations in this system, and allowing a determination of the pertinent exchange interactions in this material.

Specific heat of the dilute Ising magnet LiHoxY1-xF4.

We present specific heat data on three samples of the dilute Ising magnet LiHoxY1-xF4 with x=0.018, 0.045, and 0.080. Previous measurements of the ac susceptibility of an x=0.045 sample showed the Ho3+ moments to remain dynamic down to very low temperatures, and the specific heat was found to have unusually sharp features. In contrast, our measurements do not exhibit these sharp features in the specific heat and instead show a broad feature, for all three samples studied, which is qualitatively consistent with a spin glass state. Integrating C/T, however, reveals an increase in residual entropy with lower Ho concentration, consistent with recent Monte Carlo simulations showing a lack of spin glass transition for low x.

Long-term follow-up of a randomised trial designed to determine the need for irradiation following conservative surgery for the treatment of invasive breast cancer.

Four hundred consecutive patients aged under 70 years diagnosed with a clinical T1 or T2 breast cancer were randomised to receive post-operative radiotherapy (n = 208) or not (n = 192), and monitored to record all local recurrences, distant recurrences and deaths for up to 20 years (median 13.7 years). All patients were treated by wide local excision and adjuvant therapy [estrogen receptor (ER) positive: tamoxifen; ER negative: CMF chemotherapy]. Kaplan-Meier and log-rank test methods were used to estimate and compare survival and recurrence. The 20-year Kaplan-Meier rates for local breast recurrence were 28.6% [95% confidence interval (CI) 19.6% to 37.6%] for radiotherapy and 49.8% (95% CI 40.8% to 58.9%). There was no significant difference between the two groups with regard to disease-free or overall survival. The hazard ratio for death among women who received radiation, as compared with those that did not, was 0.91 (95% CI 0.64-1.28; P = 0.59). Therefore, post-operative radiotherapy produced a clear-cut reduction in locoregional recurrence 0.45 (0.31-0.64; P = 0.0001), but did not influence the incidence of distant metastases or time of death. However, of the 119 patients who had a local recurrence, 51 (42.8%) had a distant recurrence, whereas of the 281 without local recurrence only 59 (21%) ever had a distant recurrence. A Cox's regression analysis with local recurrence as a time-dependent variable showed a risk ratio of 5.28 (P < 0.0001). This strong relationship is dependent on the intensity of post-treatment follow-up and investigation.

Estrogen-receptor-directed neoadjuvant therapy for breast cancer: results of a randomised trial using formestane and methotrexate, mitozantrone and mitomycin C (MMM) chemotherapy.

BACKGROUND: We wanted to determine whether neoadjuvant systemic chemoendocrine therapy guided by the estrogen receptor (ER) status of the primary breast cancer, followed by conventional surgery and/or radiotherapy, reduces local and distant recurrence and improves survival compared with adjuvant treatment given conventionally postoperatively. PATIENTS AND METHODS: Two hundred ten patients with primary breast cancer (T1-T4, N0, N1-2) were randomised to receive treatment with neoadjuvant chemoendocrine therapy or conventional post-operative chemoendocrine therapy. Systemic therapy was based on the estrogen receptor (ER) status of the primary tumour obtained by trucut core biopsy. ER-negative patients received MMM chemotherapy (methotrexate (30 mg/m2), mitozantrone (7 mg/m2) and mitomycin (7 mg/m2) three-weekly for three months and ER-positive patients who were premenopausal received goserelin (3.75 mg monthly), and post menopausal women formestane (250 mg every two weeks) over three months. RESULTS: With a minimum of five years follow-up, there is no evidence of any survival benefit from the pretreatment neoadjuvant therapy regimen, with five year overall survival being 79% +/- 4.7% (neoadjuvant) and 87% +/- 3.4% (adjuvant). Similarly, there was no apparent benefit in terms of disease-free survival. There was, however, a significant reduction in the incidence of distant metastases in responders (4 of 51; 8%) compared with non-responders (17 of 49; 35%) (P < 0.01). There was a reduction in the need for surgery in responding patients with T1 and T2 tumours, since 10 of 74 (14%) had no detectable residual tumour, without any apparent increase in the risk of local or distant recurrence. CONCLUSION: In this study neoadjuvant treatment with endocrine or chemotherapy provided no obvious survival benefit to women with breast cancer. However, it does allow avoidance of surgery in some cases. Also, the patients whose tumours respond to neoadjuvant systemic therapy have a lower incidence of distant metastases after five year follow-up compared to those whose tumours fail to respond.

Assesssment of the effect of pretreatment with neoadjuvant therapy on primary breast cancer.

Patients with invasive cancer of the breast (T1-4, N0-2, M0) were assigned to pretreatment based on oestrogen receptor (ER) status; patients with ER-negative tumours received chemotherapy [mitozantrone, methotrexate and mitomycin C (MMM)] for 3 months, patients with ER-positive tumours underwent endocrine therapy [luteinising hormone releasing hormone (LHRH) agonist goserelin (leuprolide-premenopausal) or 4-hydroxyandrostenedione (formestane-post-menopausal)] for 3 months. Of the first 100 patients assessed at 3 months, 47 with ER-positive tumours had a 40.4% response (premenopausal 53.8%; post-menopausal 35%) and 53 with ER-negative tumours had a 60% response (premenopausal 57%; post-menopausal 63%). Patients with early breast cancer (T1/T2) had a complete clinical resolution in 41% (16/39) of cases after MMM and in 20% (7/35) of cases following endocrine therapy compared with 14% (2/14) advanced tumours (T3/T4) following MMM and (0/12) following endocrine therapy. However, in those patients achieving a complete clinical response, subsequent appropriate surgery showed that 16 of 19 patients (84%) had evidence of residual viable tumour on histological examination.

Prospective randomized trial of tamoxifen vs surgery in elderly patients with breast cancer.

Between 1982 and 1989, 200 patients aged 70 or over seen in one Breast Unit, who were considered to have a surgically resectable cancer of the breast were prospectively randomized to primary surgery or tamoxifen 20 mg per day. At a median follow-up of 6 years (range 3-11 years) and at the censoring date there were 61 first events in the tamoxifen group. Fifty three patients developed local relapse or progression of the cancer; three patients had simultaneous local progression or relapse and distant metastases. In addition a further five patients developed distant recurrence only. In the surgical arm there were 50 events. Thirty-six patients developed local recurrence only; eight had simultaneous local and distant recurrence. A further six patients developed distant metastases of which two subsequently developed local recurrence. There were 33 deaths in the tamoxifen group and 28 deaths in the surgical group of which 17 and 15, respectively were directly attributable to breast cancer. The disease-free interval did not differ between the two groups. Following treatment with tamoxifen, at the censoring date which was the date of last clinical examination or arbitrarily, the date of death, 39 patients had no evidence of relapse whereas in the surgical arm there were 50 patients who had no evidence of recurrence. Fifty-three patients in the tamoxifen arm had local relapse only and were available for crossover to surgery, 39 accepted surgery. Eight developed further local recurrence, 10 developed distant metastases and 21 remained free of disease. Thirty-six patients in the surgical group developed local relapse only and were available for crossover to tamoxifen. Thirty one accepted treatment with tamoxifen, 14 had progression of their local recurrence, seven developed distant metastases and 10 had no further recurrence. Thus in the tamoxifen group, 39 had no progression of their disease and a further 21 benefited from subsequent surgery: 60% in all. In the surgical group 50 had no recurrence of their disease and a further 10 benefited from subsequent tamoxifen therapy: 60% in all.

Some effects of preganglionic nerve stimulation on synaptic vesicle populations in the rat superior cervical ganglion.

1. The ;local vesicle population', namely the population of synaptic vesicles lying within a zone 0.25 mum wide adjacent to the presynaptic membrane and expressed as ;vesicles mum(-2)' has been estimated in rat superior cervical ganglia maintained in vitro for 1 h. Ganglia were either unstimulated or stimulated tetanically during the last few minutes of the in vitro period.2. Individual local vesicle populations at synapses in groups of ganglia which had received the same treatment showed an approximately normal frequency distribution.3. The technique of stimulation did not permit fixation during tetanus, but the mean local vesicle population in ganglia fixed a few seconds after 10 Hz tetani of up to 10 min duration were significantly (P < 0.001) higher than the unstimulated control value of 124.0 +/- S.E. 3.2. Ganglia fixed a few seconds after 3 min tetani at 10 Hz had a mean local vesicle population of 155.7 +/- S.E. 5.7, rising slightly but not significantly to 165.0 +/- S.E. 4.3 at 1 min and 163.1 +/- S.E. 5.2 at 2 min after tetanus. Thereafter the mean local vesicle population fell slowly, reaching control level between 10 and 20 min after tetanus.4. In terms of the vesicle hypothesis, the observations suggest that post-tetanic potentiation might arise from a closer clustering of vesicles about release areas resulting in an increase in fractional release. It is suggested that stimulation increased the local vesicle population by promoting vesicle mobilization rather than by altering the size or shape of the presynaptic terminals. The ;mobilizing agent' might be intracellular Ca(2+).5. The results appear to be consistent with those of other workers where experimental conditions and the region in which vesicles were counted were comparable.6. Alternative interpretations for the findings, not involving the vesicle hypothesis, are considered.

Identification of prostaglandins in prevertebral venous blood after preganglionic stimulation of the cat superior cervical ganglion.

1. In four out of seven experiments, prostaglandin-like activity was detected in prevertebral venous blood from the superior cervical ganglion, collected during and after preganglionic nerve stimulation.2. Prostaglandins E(1), E(2), F(2alpha) and a prostaglandin A were identified using solvent partition, column and thin-layer chromatography and bioassay techniques.3. The release of PGF(2alpha) was confirmed by combined gas chromatography-mass spectrometry.