Oct+2016

= Oct 3-Oct 7 Max, Oct 10-Oct 14 Biao Huang, Oct 17-Oct 21 Haiyuan Zou, Oct 24-Oct 28 Ahmet Kel =

= Oct 21 = [|arXiv:1610.06191] [ [|pdf], [|other] ] Interplay of non-symmorphic symmetry and spin-orbit coupling in hyperkagome spin liquids: Applications to Na 4  Ir  3  O  8    [|Biao Huang], [|Yong Baek Kim] , [|Yuan-Ming Lu]   Comments: 27 pages, 9 figures  Subjects: Strongly Correlated Electrons (cond-mat.str-el) ; Materials Science (cond-mat.mtrl-sci); Superconductivity (cond-mat.supr-con) Na 4  Ir  3  O  8  provides a material platform to study three-dimensional quantum spin liquids in the geometrically frustrated hyperkagome lattice of Ir  4 +  ions. In this work, we consider quantum spin liquids on hyperkagome lattice for generic spin models, focusing on the effects of anisotropic spin interactions. In particular, we classify possible ℤ 2  and  U ( 1 )  spin liquid states, following the projective symmetry group analysis in the slave-fermion representation. There are only three distinct ℤ 2  spin liquids, together with 2 different  U ( 1 )  spin liquids. The non-symmorphic space group symmetry of hyperkagome lattice plays a vital role in simplifying the classification, forbidding " π  -flux" or "staggered-flux" phases in contrast to symmorphic space groups. We further prove that both U ( 1 )  states and one  Z 2  state among all 3 are symmetry-protected gapless spin liquids, robust against any symmetry-preserving perturbations. Motivated by the "spin-freezing" behavior recently observed in Na 4  Ir  3  O  8  at low temperatures, we further investigate the nearest-neighbor spin model with dominant Heisenberg interaction subject to all possible anisotropic perturbations from spin-orbit couplings. We found a U ( 1 )  spin liquid ground state with spinon fermi surfaces is energetically favored over  Z 2  states. Among all spin-orbit coupling terms, we show that only Dzyaloshinskii-Moriya (DM) interaction can induce spin anisotropy in the ground state when perturbing from the isotropic Heisenberg limit. Our work paves the way for a systematic study of quantum spin liquids in various materials with a hyperkagome crystal structure.

= Oct 20 = [|arXiv:1610.05810] [ [|pdf], [|other] ] Dynamical Chern-Simons Theory in the Brillouin Zone [|Biao Lian], [|Cumrun Vafa] , [|Farzan Vafa] , [|Shou-Cheng Zhang]   Comments: 13 pages, 2 figures  Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ; Superconductivity (cond-mat.supr-con); High Energy Physics - Theory (hep-th) Berry connection is conventionally defined as a static gauge field in the Brillouin zone. Here we show that for three-dimensional (3d) time-reversal invariant superconductors, a generalized Berry gauge field behaves as a dynamical fluctuating field of a Chern-Simons gauge theory. The gapless nodal lines in the momentum space play the role of Wilson loop observables, while their linking and knot invariants modify the gravitational theta angle. This angle induces a topological gravitomagnetoelectric effect where a temperature gradient induces a rotational energy flow. We also show how topological strings may be realized in the 6 dimensional phase space, where the physical space defects play the role of topological D-branes.

= Oct 19 = [|arXiv:1610.05398] [ [|pdf], [|other] ] Many body localization in two dimensional square and triangular lattices [|L. Gonzalez-Garcia], [|S. F. Caballero-Benitez] , [|R. Paredes]   Comments: 6 pages, 7 Figures  Subjects: Quantum Gases (cond-mat.quant-gas) ; Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph) Ultracold interacting Bose atoms placed in disordered two dimensional optical lattices with square and triangular symmetries are found to be localized above a certain disorder strength amplitude. From a Gross-Pitaevskii mean analysis we determine the localization length as a function of the disorder strength and investigate the energy spectrum in terms of the disorder magnitude. We found that the localization length is observed to decrease faster in triangular geometries than in square ones. In the presence of a harmonic confinement localization is observed at the center of the trap. The analysis of the energy spectrum reveals that discrete energy levels acquire a finite width that is always smaller than the distance among energy levels.

= = = = = Oct 18 = =  [|arXiv:1610.04632] [ [|pdf], [|other] ]  = Electron Doping a Kagome Spin Liquid [|Z.A. Kelly], [|M.J. Gallagher] , [|T.M. McQueen]   Journal-ref: Phys. Rev. X 6, 041007 13 October 2016 Subjects: Strongly Correlated Electrons (cond-mat.str-el)  Herbertsmithite, ZnCu  3  (OH)  6  Cl  2  , is a two dimensional kagom\'{e} lattice realization of a spin liquid, with evidence for fractionalized excitations and a gapped ground state. Such a quantum spin liquid has been proposed to underlie high temperature superconductivity and is predicted to produce a wealth of new states, including a Dirac metal at  1 / 3 rd electron doping. Here we report the topochemical synthesis of electron-doped ZnLi  x Cu  3  (OH)  6  Cl  2  <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> from <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> x  <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">0 to x <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">1.8 ( <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> 3 / 5  <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">th per Cu <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> 2 +  <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">). Contrary to expectations, no metallicity or superconductivity is induced. Instead, we find a systematic suppression of magnetic behavior across the phase diagram. Our results demonstrate that significant theoretical work is needed to understand and predict the role of doping in magnetically frustrated narrow band insulators, particularly the interplay between local structural disorder and tendency toward electron localization, and pave the way for future studies of doped spin liquids. = = = = = Oct 17 =

[|arXiv:1610.04300] [ [|pdf], [|other] ] Intertwined Order in a Frustrated 4-leg t − J  Cylinder  [|John F. Dodaro], [|Hong-Chen Jiang] , [|Steven A. Kivelson] Comments: 14 pages Subjects: Strongly Correlated Electrons (cond-mat.str-el) <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">We report a density-matrix renormalization group study of the <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> t <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">- <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> J  <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> model with nearest ( <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> t 1  <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> & <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> J 1  <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">) and next-nearest ( <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> t 2  <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> & <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> J 2  <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">) interactions on a 4-leg cylinder with concentration <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> δ = 1 / 8  <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> of doped holes. We observe an astonishingly complex interplay between uniform <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> d <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">-wave superconductivity (SC) and strong spin and charge density wave ordering tendencies (SDW and CDW). Depending on parameters, the CDWs can be commensurate with period 4 or 8. By comparing the charge ordering vectors with <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> 2 k F <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">, we rule out Fermi surface nesting-induced density wave order in our model. Magnetic frustration (i.e. <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> J 2 / J 1 ∼ 1 / 2 <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">) significantly quenches SDW correlations with little effect on the CDW. Typically, the SC order is strongly modulated at the CDW ordering vector and exhibits <span class="MathJax" style="font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> d <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">-wave symmetry around the cylinder. There is no evidence of a near-degenerate tendency to pair-density wave (PDW) ordering, charge 4e SC, or orbital current order.