In completing one discovery, we never fail to get an imperfect knowledge of others of which we could have no idea before, so that we cannot solve one doubt without creating several new ones.
Joseph Priestley (1786)

Email: pye [AT] pitp.ca

In each fundamental branch of physics, we are making efforts in understanding the nature of "vacuum quantum state" which is governed by:

(1)
\begin{align} \hat{\mathcal{H}}|Vacuum\rangle=i\partial_t|Vacuum\rangle \end{align}

for the reason that various "patterns" in $|Vacuum\rangle$ determine the orders/entanglement of condensed matter materials and universe.

##### (9/2003-7/2007) undergraduate, Bachelor of Science, Physics

in Department of Physics, Sun Yat-sen University (SYSU), Guangzhou, China
Seminar Supervisor: Prof. Xiang-Qian Luo
Research area: analytic aspect in Lattice Gauge Theory

##### (Since 9/2007-7/2012) PhD, Physics

in Institute for Advanced Study (IASTU), Tsinghua University, Beijing, China
PhD Supervisor: Prof. Zheng-Yu Weng
Research area: Condensed Matter Theory
PhD Thesis title: Quantum Magnetism and High-Temperature Superconductivity in t-J model

## OTHER EXPERIENCE

• (Fall/2008) Teaching Assistant. Course: College Physics.
• (Spring/2009) Teaching Assistant. Course: Quantum and Statistical Physics.
• (3/2011)，Contributed talk, 2011 March Meeting of American Physical Society in Dallas, Texas, USA.
• (Since 3/2011-4/2011) Visiting Scholar in Stanford University, California, USA.
• (12/2011-1/2012) Visiting Student in Stanford University, California, USA.
• (9/2011-12/2011) attendee of topomat11 workshop in KITP (Kavli Institute for Theoretical Physics) in UCSB (University of California at Santa Barbara), Santa Barbara, CA, USA.
• (11/2012) UIUC-PI joint workshop, Institute for Condensed Matter Physics (ICMT), UIUC, Urbana-Champaign, IL, USA.
• (2/2013) Institute for Advanced Study, Tsinghua University.
• (3/2013) 2013 March Meeting, Baltimore, ML, USA.
• (3/2013) Seminar invited talk, Stanford University, CA, USA.
• (5/2013) Invited talk, Conference "Emergence and Entanglement II", Perimeter Institute, Waterloo, Canada

• Tsinghua Outstanding PhD Dissertation (Major Award) (Jul. 2012)
• Graduation with Distinction of Beijing City (Jul. 2012)
• Tsinghua Excellent Graduate Student Scholarship (Major Award) (Tsinghua, Oct. 2011)
• Tsinghua Scholarship for Overseas Graduate Studies (Tsinghua, July, 2011)
• Tsinghua Excellent Graduate Student Scholarship (Minor Award) (Tsinghua, Oct., 2010)
• The Best Poster Award in Annual Meeting of Chinese Physical Society (Nankai Univ., Sep. 2010)
• C. N. Yang Fellowship (Tsinghua, 13 Sep., 2007)
• 2007 SYSU Graduation with Distinction (SYSU Degree Ceremony, July, 2007)
• Japan Sumitomo Corporation Scholarship (SYSU, Sep. 2006)
• SYSU Excellence Award (Major Award) (SYSU, Sep. 2006)
• SYSU Excellence Award (Minor Award) (SYSU, Sep. 2005)
• SYSU Excellence Award (Third-Class Award) (SYSU, Sep. 2004).

## RESEARCH INTERESTS

I show interests in strongly correlated electron systems as well as quantum field theory. Currently, I am concentrating on the following topics:

• Superconductivity in strongly correlated systems. exotic phases in doped Mott insulators.
• Quantum field theory in low dimensions; topological quantum field theory.
• Symmetry-Protected Topological Phases (SPT).

etc.

## PUBLICATIONS AND PREPRINTS

[YeXX], XX indicates the year in which the first version is finalized.

##### [Ye13a] PY and Xiao-Gang Wen, [arXiv:1303.3572] [CITATION] [submitted]

Title: A 3-dimensional bosonic topological insulator and its exotic electromagnetic response
Abstract: Recently, many new types of bosonic symmetry-protected topological phases, including bosonic topological insulators, were predicted using group cohomology theory. The bosonic topological insulators have both U(1) symmetry (particle number conservation) and time-reversal symmetry, described by symmetry group $U(1)\rtimes Z_2^T$. In this paper, we propose a projective construction of three-dimensional correlated gapped bosonic state with $U(1)\rtimes Z_2^T$ symmetry. The gapped bosonic insulator is formed by eight kinds of charge-1 bosons. We show that, in our bosonic state, an electromagnetic monopole with a unit magnetic charge is fermionic while an electromagnetic dyon with a unit magnetic charge and a unit electric charge is bosonic. This indicates that the constructed bosonic state is a non-trivial bosonic topological insulator, since in a trivial bosonic Mott insulator, the monopole is bosonic while the dyon is fermionic. We also constructed a three-dimensional correlated gapless bosonic insulator with $U(1)\rtimes Z_2^T$ symmetry, that has two emergent gapless U(1) gauge fields, and excitations with fractional gauge charges for both the emergent and electromagnetic gauge fields. Both bosonic insulators can have protected conducting surface states. The gapless boundary excitations of the gapless bosonic insulator can even be fermionic.

##### [Ye12c] PY and Xiao-Gang Wen, [arXiv:1212.2121] [CITATION] [to appear in Phys. Rev. B]

Title: Projective construction of two-dimensional symmetry-protected topological phases with U(1) / SO(3) / SU(2) symmetries
Abstract: We propose a general approach to construct symmetry protected topological (SPT) states (i.e. the short-range entangled states with symmetry) in 2D spin/boson systems on lattice. In our approach, we fractionalize spins/bosons into different fermions, which occupy nontrivial Chern bands. After the Gutzwiller projection of the free fermion state obtained by filling the Chern bands, we can obtain SPT states on lattice. In particular, we constructed a U(1) SPT state of a spin-1 model, a SO(3) SPT state of a boson system with spin-1 bosons and spinless bosons, and a SU(2) SPT state of a spin-1/2 boson system. By applying the “spin gauge field” which directly couples to the spin density and spin current of $S^z$ components, we also calculate the quantum spin Hall conductance in each SPT state. The projective ground states can be further studied numerically in the future by variational Monte Carlo etc.

##### [Ye12b] PY and Qing-Rui Wang, [arXiv:1206.0258] [CITATION] [submitted]

Title: Monopoles, confinement and charge localization in the t-J model with dilute holes
Abstract: We present a quantum field theoretic description on the t-J model on a square lattice with dilute holes (i.e. near half-filling), based on the compact mutual Chern-Simons gauge theory. We show that, due to the presence of non-perturbative monopole plasma configuration from the antiferromagnetic background, holons (carrying electric charge) are linearly confined and strongly localized even without extrinsic disorder taken into account. Accordingly, the translation symmetry is spontaneously broken at ground state. This quantum phenomenon has been recently unveiled in an atomic scale STM experimental probe [C. Ye et al. arxiv: 1201.0342] and DMRG numerical simulation [Z. Zhu et al. arxiv: 1205.5277]. Such an exotic localization is distinct from Anderson localization and essentially rooted in intrinsic Mott physics of t-J model. Finally, a finite-temperature phase diagram is proposed. The metal-insulator transition observed in in-plane resistivity measurement is identified to a confinement-deconfinement transition from the perspective of gauge theory. The transition is characterized by the order parameter "Polyakov-line".

##### [Ye12a] Chao-Xing Liu, PY, and Xiao-Liang Qi, [arXiv:1204.6551] [CITATION] [submitted]

Title: Chiral gauge field and axial anomaly in a Weyl-semi-metal
Abstract: Weyl fermions are two-component chiral fermions in (3+1)-dimensions. When coupled to a gauge field, the Weyl fermion is known to have an axial anomaly, which means the current conservation of the left-handed and right-handed Weyl fermions cannot be preserved separately. Recently, Weyl fermions have been proposed in condensed matter systems named as "Weyl semi-metals". In this paper we propose a Weyl semi-metal phase in magnetically doped topological insulators, and study the axial anomaly in this system. We propose that the magnetic fluctuation in this system plays the role of a "chiral gauge field" which minimally couples to the Weyl fermions with opposite charges for two chiralities. We study the anomaly equation of this sytem and discuss its physical consequences, including one-dimensional chiral modes in a ferromagnetic vortex line, and a novel plasmon-magnon coupling.

##### [Ye11b] PY, Long Zhang, and Zheng-Yu Weng, Phys. Rev. B 85, 205142 (2012). [arXiv:1110.0125] [CITATION] [Published]

Title: Superconductivity in mutual Chern-Simons gauge theory
Abstract: In this work, we present a topological characterization of superconductivity in a prototype electron fractionalization model for doped Mott insulators. In this model, spinons and holons are coupled via the mutual Chern-Simons gauge fields. We obtain a low-lying effective description of the collective current fluctuations by integrating out the matter fields, which replaces the conventional Ginzburg-Landau action to describe the generalized rigidity of superconductivity. The superconducting phase coherence is essentially characterized by a topological order parameter related to a Gaussian linking number, and an experiment is proposed to probe this topological property. We further show that a gauge-neutral fermionic mode can naturally emerge in this model, which behaves like a Bogoliubov quasiparticle.

##### [Ye11a] PY, Chu-Shun Tian, Xiao-Liang Qi, and Zheng-Yu Weng, Nucl. Phys. B 854, 815 (2012). [arXiv:1106.1223] [CITATION] [Published]

Title: Electron fractionalization and unconventional order parameters of the t-J model [ Note added: long version of Ye10]
Abstract: In the t–J model, the electron fractionalization is unique due to the non-perturbative phase string effect. We formulated a lattice field theory taking this effect into full account. Basing on this field theory, we introduced a pair of Wilson loops which constitute a complete set of order parameters determining the phase diagram in the underdoped regime. We also established a general composition rule for electric transport expressing the electric conductivity in terms of the spinon and the holon conductivities. The general theory is applied to studies of the quantum phase diagram. We found that the antiferromagnetic and the superconducting phases are dual: in the former, holons are confined while spinons are deconfined, and vice versa in the latter. These two phases are separated by a novel phase, the so-called Bose-insulating phase, where both holons and spinons are deconfined and the system is electrically insulating.

##### [Ye10] PY, Chu-Shun Tian, Xiao-Liang Qi, and Zheng-Yu Weng, Phys. Rev. Lett. 106, 147002 (2011). [arXiv:1007.2507] [CITATION] [Published]

Title: Confinement-deconfinement interplay in quantum phases of doped Mott insulators
Abstract: In the t-J model, the electron fractionalization is dictated by the phase string effect. We find that in the underdoped regime, the antiferromagnetic and superconducting phases are dual: in the former, holons are confined while spinons are deconfined, and vice versa in the latter. These two phases are separated by a novel phase, the so-called Bose-insulating phase, where both holons and spinons are deconfined. A pair of Wilson loops was found to constitute a complete set of order parameters determining this zero-temperature phase diagram. The quantum phase transitions between these phases are suggested to be of non-Landau-Ginzburg-Wilson type.

##### [Ye07] PY, X.-L. Yu, Y. Guan, and X.-Q. Luo, Mod. Phys. Lett. A 22, 547 (2007). [CITATION] [Published]

Title: Overlap fermions in the strong coupling limit
Abstract: We analyze the overlap fermion formulation expanded in powers of a hopping parameter in the strong coupling limit. The mass of the quasi-Goldstone pion is obtained. A random walk representation for the overlap fermion propagator is developed, to conclude that the expanded overlap fermion formulation, however, cannot be totally solve the fermion-doubling problem.

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