Mar 2018

Mar 1- Mar 5 Zehan Li, Mar 6-Mar 10 Jiansong Pan, Mar 11-Mar 15 Ahmet Keles, Mar 16-Mar 20 Max Aarzamazovs, Mar 21-Mar 25 Xuguang Yue, Mar 26-Mar 30 Biao Huang, Mar 31 Haiyuan Zou

Mar 5

arXiv:1802.10533 [pdf, other]
Modern Theory for the Orbital Moment in a Superconductor
Joshua Robbins, James F. Annett, Martin Gradhand
Subjects: Superconductivity (cond-mat.supr-con)
The chiral p-wave superconducting state is comprised of spin triplet Cooper pairs carrying a finite orbital angular momentum. For the case of a periodic lattice, calculating the net magnetisation arising from this orbital component presents a challenge as the circulation operator ˆr × pˆ is not well defined in the Bloch representation. This difficulty has been overcome in the normal state, for which a modern theory is firmly established. Here, we derive the extension of this normal state approach, generating a theory which is valid for a general superconducting state, and go on to perform model calculations for a chiral p-wave state in Sr2RuO4. The results suggest that the magnitude of the elusive edge current in Sr2RuO4 is finite, but lies below experimental resolution. This provides a possible solution to the long-standing controversy concerning the gap symmetry of the superconducting state in this material.


 Mar 6

arXiv:1803.01803 [pdf, other]
Formation of a spin texture in a quantum gas coupled to a cavity
M. Landini, N. Dogra, K. Kröger, L. Hruby, T. Donner, T. Esslinger
Subjects: Quantum Gases (cond-mat.quant-gas)

We observe cavity mediated spin-dependent interactions in an off-resonantly driven multi-level atomic Bose-Einstein condensate that is strongly coupled to an optical cavity. Applying a driving field with adjustable polarization, we identify the roles of the scalar and the vectorial components of the atomic polarizability tensor for single and multi-component condensates. Beyond a critical strength of the vectorial coupling, we observe a spin texture in a condensate of two internal states, providing perspectives for global dynamic gauge fields and self-consistently spin-orbit coupled gases.

arXiv:1803.01411 (cross-list from cond-mat.str-el) [pdf, other]
Topological Sachdev-Ye-Kitaev Model
Pengfei Zhang, Hui Zhai
Comments: 6 pages, 5 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas)



In this letter we construct a large-N exactly solvable model to study the interplay between interaction and topology, by connecting Sacheve-Ye-Kitaev (SYK) model with constant hopping. The hopping forms a band structure that can exhibit both topological trivial and nontrivial phases. Starting from a topologically trivial insulator with zero Hall conductance, we show that interaction can drive a phase transition to topological nontrivial insulator with quantized non-zero Hall conductance, and a single gapless Dirac fermion emerges when the interaction is fine tuned to the critical point. The finite temperature effect is also considered and we show that the topological phase with stronger interaction is less stable against temperature. Our model provides a concrete example to illustrate interacting topological phases and phase transition, and can shed light on similar problems in physical systems.


 Mar 7

arXiv:1803.01920 [pdf, ps, other]
Designer Spatial Control of Interactions in Ultracold Gases
N. Arunkumar, A. Jagannathan, J. E. Thomas
Comments: 7 pages, 3 figuresSubjects: Quantum Gases (cond-mat.quant-gas)
Designer optical control of interactions in ultracold atomic gases has wide application, from creating new quantum phases to modeling the physics of black holes. We demonstrate spatial control of interactions in a two-component cloud of 6Li fermions, using electromagnetically induced transparency (EIT) to create a "sandwich" of resonantly and weakly interacting regions. Interaction designs are imprinted on the trapped cloud by two laser beams and manipulated with just MHz changes in the frequency of one beam. We employ radio-frequency spectroscopy to measure the imprinted 1D spatial profiles of the local mean-field energy shifts and to demonstrate that the tuning range of the scattering length is the same for both optical and magnetic control. All of the data are in excellent agreement with our continuum-dressed state theoretical model of optical control, which includes both the spatial and momentum dependence of the interactions.

arXiv:1803.02293 (cross-list from physics.atom-ph) [pdf, ps, other]
Pinning Transition of Bose-Einstein Condensates in Optical Ring Resonators
S. C. Schuster, P. Wolf, D. Schmidt, S. Slama, C. Zimmermann
Comments: 4 pages, 3 figuresSubjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas); Optics (physics.optics)
We experimentally explore the stability of Bose-Einstein condensates inside an optical ring resonator with additional periodic pinning potential. Beyond a critical resonator detuning the system undergoes a transition to a new stable phase. Phase diagrams and quench curves are recorded and described by numerical simulations. We also discuss a physical explanation based on a geometrical interpretation of the underlying nonlinear equations of motion

arXiv:1803.01876 (cross-list from cond-mat.mes-hall) [pdf, ps, other]
Edge states and topological invariants of non-Hermitian systems
Shunyu Yao, Zhong Wang
Comments: 8 pages, 6 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Other Condensed Matter (cond-mat.other); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Optics (physics.optics)

For Hermitian systems, the creation or annihilation of topological edge modes is accompanied by the gap closing of Bloch Hamiltonian; for non-Hermitian systems, however, the edge-state transition points can differ from the gap closing points of Bloch Hamiltonian, which indicates breakdown of the usual bulk-boundary correspondence. We study this intriguing phenomenon via exactly solving a prototype model, namely the onedimensional non-Hermitian Su-Schrieffer-Heeger model. The solution shows that the usual Bloch waves give way to eigenstates localized at the ends of an open chain, and the Bloch Hamiltonian is not the appropriate bulk side of bulk-boundary correspondence. It is shown that the standard Brillouin zone (a unit circle for one-dimensional systems) is replaced by a deformed one (a non-unit circle for the solved model), in which topological invariants can be precisely defined, embodying an unconventional bulk-boundary correspondence. This topological invariant correctly predicts the edge-state transition points and the number of topological edge modes. The theory is of general interest to topological aspects of non-Hermitian systems.

Mar 8



arXiv:1803.02456 [pdf, other]
Observation and uses of position-space Bloch oscillations in an ultracold gas
Zachary A. Geiger, Kurt M. Fujiwara, Kevin Singh, Ruwan Senaratne, Shankari V. Rajagopal, Mikhail Lipatov, Toshihiko Shimasaki, Rodislav Driben, Vladimir V. Konotop, Torsten Meier, David M. Weld
Comments: 5 pages, 6 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)
We report the direct observation and characterization of position-space Bloch oscillations using an ultracold gas in a tilted optical lattice. While Bloch oscillations in momentum space are a common feature of optical lattice experiments, the real-space center-of-mass dynamics are typically too small to resolve. Tuning into the regime of rapid tunneling and weak force, we observe realspace Bloch oscillation amplitudes of hundreds of lattice sites, in both ground and excited bands. We demonstrate two unique capabilities enabled by tracking of Bloch dynamics in position space: measurement of the full position-momentum phase-space evolution during a Bloch cycle, and direct imaging of the lattice band structure. These techniques, along with the ability to exert long-distance coherent control of quantum gases without modulation, may open up new possibilities for quantum control and metrology.

Mar 9

arXiv:1803.02904 (cross-list from cond-mat.quant-gas) [pdf, other]
Renormalization group analysis of dipolar Heisenberg model on square lattice
Ahmet Keles, Erhai Zhao
Comments: 9 pages, 4 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)



We present a detailed functional renormalization group analysis of spin-1/2 dipolar Heisenberg model on square lattice. This model is similar to the well known J1-J2 model and describes the pseudospin degrees of freedom of polar molecules confined in deep optical lattice with long-range anisotropic dipole-dipole interactions. Previous study of this model based on tensor network ansatz indicates a paramagnetic ground state for certain dipole tilting angles which can be tuned in experiments to control the exchange couplings. The tensor ansatz formulated on a small cluster unit cell is inadequate to describe the spiral order, and therefore the phase diagram at high azimuthal tilting angles remains undetermined. Here we obtain the full phase diagram of the model from numerical pseudofermion functional renormalization group calculations. We show that an extended quantum paramagnetic phase is realized between the N\'{e}el and stripe/spiral phase. In this region, the spin susceptibility flows smoothly down to the lowest numerical renormalization group scales with no sign of divergence or breakdown of the flow, in sharp contrast to the flow towards the long-range ordered phases. Our results provide further evidence that the dipolar Heisenberg model is a fertile ground for quantum spin liquids.

arXiv:1803.02838 (cross-list from cond-mat.dis-nn) [pdf, other]
Beyond many-body localized states in a spin-disordered Hubbard model with pseudo-spin symmetry
Xiongjie Yu, Di Luo, Bryan K. Clark
Comments: 12 pages, 18 figures
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Strongly Correlated Electrons (cond-mat.str-el)




A prime characterization of many-body localized (MBL) systems is the entanglement of their eigenstates; in contrast to the typical ergodic phase whose eigenstates are volume law, MBL eigenstates obey an area law. In this work, we show that a spin-disordered Hubbard model has both a large number of area-law eigenstates as well as a large number of eigenstates whose entanglement scales logarithmically with system size (log-law). This model, then, is a microscopic Hamiltonian which is neither ergodic nor many-body localized. We establish these results through a combination of analytic arguments based on the eta-pairing operators combined with a numerical analysis of eigenstates. In addition, we describe and simulate a dynamic time evolution approach starting from product states through which one can separately probe the area law and log-law eigenstates in this system.