Signatures of a gapless quantum spin liquid in the Kitaev material Na3_3Co2−x_{2-x}Znx_xSbO6_6

The honeycomb-lattice cobaltate Na$_3$Co$_2$SbO$_6$ has recently been proposed to be a proximate Kitaev quantum spin liquid~(QSL) candidate. However, non-Kitaev terms in the Hamiltonian lead to a zigzag-type antiferromagnetic~(AFM) order at low temperatures. Here, we partially substitute magnetic Co$^{2+}$ with nonmagnetic Zn$^{2+}$ and investigate the chemical doping effect in tuning the magnetic ground states of Na$_3$Co$_{2-x}$Zn$_x$SbO$_6$. X-ray diffraction characterizations reveal no structural transition but quite tiny changes on the lattice parameters over our substitution range $0\leq x\leq0.4$. Magnetic susceptibility and specific heat results both show that AFM transition temperature is continuously suppressed with increasing Zn content $x$ and neither long-range magnetic order nor spin freezing is observed when $x\geq0.2$. More importantly, a linear term of the specific heat representing fermionic excitations is captured below 5~K in the magnetically disordered regime, as opposed to the $C_{\rm m}\propto T^3$ behavior expected for bosonic excitations in the AFM state. Based on the data above, we establish a magnetic phase diagram of Na$_3$Co$_{2-x}$Zn$_x$SbO$_6$. Our results indicate the presence of gapless fractional excitations in the samples with no magnetic order, evidencing a potential QSL state induced by doping in a Kitaev system.Comment: 10 pages, 5 figure

Fully gapped topological surface states in Bi2_2Se3_3 films induced by a d-wave high-temperature superconductor

Topological insulators are a new class of materials, that exhibit robust gapless surface states protected by time-reversal symmetry. The interplay between such symmetry-protected topological surface states and symmetry-broken states (e.g. superconductivity) provides a platform for exploring novel quantum phenomena and new functionalities, such as 1D chiral or helical gapless Majorana fermions, and Majorana zero modes which may find application in fault-tolerant quantum computation. Inducing superconductivity on topological surface states is a prerequisite for their experimental realization. Here by growing high quality topological insulator Bi$_2$Se$_3$ films on a d-wave superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ using molecular beam epitaxy, we are able to induce high temperature superconductivity on the surface states of Bi$_2$Se$_3$ films with a large pairing gap up to 15 meV. Interestingly, distinct from the d-wave pairing of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$, the proximity-induced gap on the surface states is nearly isotropic and consistent with predominant s-wave pairing as revealed by angle-resolved photoemission spectroscopy. Our work could provide a critical step toward the realization of the long sought-after Majorana zero modes.Comment: Nature Physics, DOI:10.1038/nphys274

Inpatient Complications, Charges, and Length of Stay for Surgical Patients with Class III Malocclusions

Objectives: 1. To determine high risk factors for complications of inpatient orthognathic surgeries among patients with Class III malocclusions. 2. To provide an overview of hospital charges and length of stay for inpatient orthognathic surgeries among patients with Class III malocclusions. Methods: Any patient with Class III malocclusions but no craniofacial anomalies in the Nationwide Inpatient Sample (NIS) who underwent at least one of the orthognathic surgeries (based on International Classification of Disease-9-Clinical Modification procedure codes) between year 2006-2014 were included and examined for various complications. High occurrence complications were further studied by multivariable regression analysis to detect associations between different factors and the occurrence of complications. Results: Weighted total of 38,596 hospital stays were included in this study. The mean length of stay (LOS) for patients was 1.78 days while the median was 0.99 day. The mean total charges were $56,200 and the median of total hospital charges was$48,240. Maxillary hypoplasia alone (63%) was the most common reported diagnosis for in-hospital orthognathic surgeries in the U.S. for Class III malocclusions during 2006-2014. The overall complication rate among these patients was 2.28%. The two most frequent complications were hemorrhage (0.96%) and iatrogenic complications (0.75%). While having comorbid conditions increased the occurrence of both hemorrhage and iatrogenic complications, being female had a protective effect against both hemorrhage and iatrogenic complications. Conclusions: Some patient-related factors had significant association with the occurrence of complications. Years of admission were also shown to be related to the occurrence of complications. Hospital-related factors did not show significant association with the occurrence of complications