arXiv subjects

Mingyuan Sun

Publications and source records attributed to Mingyuan Sun.

24 records · Page 2Linked to original sources

arXiv2018

Magnetic Manifestation of Discrete Scaling Symmetry in Dirac Semimetals

Two-dimensional and three-dimensional massless Dirac fermions can form a sequence of quasibound states with an attractive charged impurity. These quasibound states exhibit a discrete scaling symmetry, i.e., the energy ratio between two successive states is a constant. Through the calculation of the energy spectrum directly, we find that in two dimension an applied magnetic field can shift or even destroy the quasibound states around the Dirac point and their discrete scaling symmetry disappears. However, as the magnetic field increases, the remaining quasibound states are pushed up to the Dirac point. When one quasibound state is close to the Dirac point, the spectrum is modified significantly, due to the resonant scattering. The magnetic oscillation of the spectrum displays the same discrete scaling symmetry as the quasibound state does in zero magnetic field. This phenomenon also occurs in the quantum limit of three-dimensional Dirac semimetals, where the system becomes quasi one-dimensional essentially. Our theoretical analysis are in good agreement with the recent experimental observations.

cond-mat.mes-hall↗

arXiv2018

Landau Level to Efimov-like Bound State Crossover in Two-dimensional Dirac Semimetals

In two-dimensional Dirac semimetals, massless Dirac fermions can form a series of Efimov-like quasibound states in an attractive Coulomb potential. In an applied magnetic field, these quasibound states can become bound states around the Dirac point, due to the energy gap between two successive Landau levels. Through the calculation of the energy spectrum directly, we show that there exists a crossover from the Landau level to the bound state as the magnetic field increases. Because of the decreasing magnetic length, the deep quasibound states are pushed up to the Dirac point relatively and transformed into bound states gradually. Furthermore, the magnetic positions of the emerging bound states in the crossovers obey a geometric scaling law, which can be regarded as an analogy of the radial law in the Efimov effect. We extend our analysis to massless three-component fermions, which also demonstrate this phenomenon. Our results show the universality of fermions with linear dispersion in two dimension and pave a way for the future experimental exploration.

cond-mat.mes-hall↗

arXiv2017

Controlled Transport between Fermi Superfluids Through a Quantum Point Contact

Recent advances in experimental techniques allow one to create a quantum point contact between two Fermi superfluids in cold atomic gases with a tunable transmission coefficient. In this Letter we propose that three distinct behaviors of charge transports between two Fermi superfluids can be realized in this single setup, which are the multiple Andreev reflection, the self-trapping and the Josephson oscillation. We investigate the dynamics of atom number difference between two reservoirs for different initial conditions and different transmission coefficients, and present a coherent picture of how the crossover between different regimes takes place. Our results can now be directly verified in current experimental system.

cond-mat.quant-gas↗

arXiv2017

Enhancing the Efimov correlation in Bose polarons with large mass imbalance

We study the effect of Efimov physics (in the few-body sector) to the spectral response of Bose polaron, a many-body system consisting of an impurity immersed in a bath of bosonic atoms. We find that the Efimov correlation can be greatly enhanced by increasing the mass ratio between the bosons and the impurity, which results in visible signatures in the rf spectrum of the polaron. Using a diagrammatic approach up to the third-order virial expansion, we show how the mass imbalance and the enhanced three-body effect modify the line shape and the width of the polaron spectrum. Moreover, we study the effect of a finite boson-boson interaction to the spectrum. Taking the realistic system of Li impurities immersed in Cs bosons with a positive Cs-Cs scattering length, we find a visible Efimov branch, which is associated with the second lowest Efimov trimer, in the polaron spectrum. In particular, by adjusting the boson density the Efimov branch can greatly hybridize with the attractive polaron branch leading to the spectrum broadening near their avoided level crossing. Our results can be directly probed in the cold atoms experiments of Li-Cs and Li-Rb Bose polarons.

cond-mat.quant-gas↗

arXiv2017

Visualizing Efimov Correlations in the Bose Polaron

The Bose polaron is a quasi-particle of an impurity dressed by surrounding bosons. In few-body physics, it is known that two identical bosons and a third distinguishable particle can form a sequence of Efimov bound states in the vicinity of inter-species scattering resonance. On the other hand, in the Bose polaron system with an impurity atom embedded in many bosons, no signature of Efimov physics has been reported in the existing spectroscopy measurements up to date. In this work, we propose that a large mass imbalance between a light impurity and heavy bosons can help produce visible signatures of Efimov physics in such a spectroscopy measurement. Using the diagrammatic approach in the Virial expansion to include three-body effects from pair-wise interactions, we determine the impurity self-energy and its spectral function. Taking $^{6}$Li-$^{133}$Cs\ system as a concrete example, we find two visible Efimov branches in the polaron spectrum, as well as their hybridizations with the attractive polaron branch. We also discuss the general scenarios for observing the signature of Efimov physics in polaron systems. This work paves the way for experimentally exploring intriguing few-body correlations in a many-body system in the near future.

cond-mat.quant-gas↗

arXiv2015

High-temperature expansion for interacting fermions

We present a general method for the high-temperature expansion of the self-energy of interacting particles. Though the method is valid for fermions and bosons, we illustrate it for spin one half fermions interacting via a zero range potential, in the Bose Einstein Condensate - Bardeen Cooper Schrieffer (BEC-BCS) crossover. The small parameter of the expansion is the fugacity z. Our results include terms of order z and z^2, which take into account respectively two and three body correlations. We give results for the high temperature expansion of Tan's contact at order z^3 in the whole BEC-BCS crossover. We apply our method to calculate the spectral function at the unitary limit. We find new structures which were overlooked by previous approaches, which included only two body correlations. This shows that including three-body correlations can play an important role in the structures of the spectral function.

cond-mat.quant-gas↗