Browsing by Author "Chou, Po-Hao"

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Emergence of a Fermionic Finite-Temperature Critical Point in a Kondo Lattice
(2016-04-27)
Chou, Po-Hao
;
Zhai, Liang-Jun
;
Chung, Chung-Hou
;
Mou, Chung-Yu
;
Lee, Ting-Kuo
The underlying Dirac point is central to the profound physics manifested in a wide class of materials. However, it is often difficult to drive a system with Dirac points across the massless fermionic critical point. Here by exploiting screening of local moments under spin-orbit interactions in a Kondo lattice, we show that below the Kondo temperature, the Kondo lattice undergoes a topological transition from a strong topological insulator to a weak topological insulator at a finite temperature T-D. At T-D, massless Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our analysis indicates that the emergent relativistic symmetry dictates nontrivial thermal responses over large parameter and temperature regimes. In particular, it yields critical scaling behaviors both in magnetic and transport responses near T-D.
Enhanced quantum oscillations in Kondo insulators
(2020-03-02)
Lu, Yen-Wen
;
Chou, Po-Hao
;
Chung, Chung-Hou
;
Lee, Ting-Kuo
;
Mou, Chung-Yu
Quantum oscillations have long been regarded as the manifestation of the Fermi surface in metals. However, they were recently observed in Kondo insulators. We examine the Kondo screening due to Landau levels in Kondo insulators. It is shown that, even for large Kondo insulating gaps, appreciable amplitudes of quantum oscillations that are consistent with experimental observations are present both in magnetization and resistivity. Specifically, we show that, due to the periodic alignment between the Landau levels in the conduction and the f-orbit electrons, the Kondo screening itself undergoes oscillations so that the electronic structure oscillates with the magnetic field. Our results explain main features of quantum oscillations observed in experiments. They indicate that the nonrigidity of the electronic structure results in observable quantum oscillation Kondo insulators. This effect provides a way to probe the Fermi surface geometry of insulators.
Strain-induced superconducting pair density wave states in graphene
(2018-11-02)
Xu, Feng
;
Chou, Po-Hao
;
Chung, Chung-Hou
;
Lee, Ting-Kuo
;
Mou, Chung-Yu
Graphene is known to be nonsuperconducting. However, surprising superconductivity is recently discovered in a flat band in a twisted bilayer graphene. Here, we show that superconductivity can be more easily realized in topological flat bands induced by strain in graphene through periodic ripples. Specifically, it is shown that by including correlation effects, the chiral d-wave superconductivity can be stabilized under strain even for slightly doped graphene. The chiral d-wave superconductivity generally coexists with charge density waves (CDW) and pair density waves (PDW) of the same period. Remarkably, a pure PDW state with doubled period that coexists with the CDW state is found to emerge at a finite-temperature region under reasonable strain strength. The emergent PDW state is shown to be superconducting with nonvanishing superfluid density, and it realizes the long-sought-after superconducting states with nonvanishing center-of-mass momentum for Cooper pairs.
TACCO, a Database Connecting Transcriptome Alterations, Pathway Alterations and Clinical Outcomes in Cancers
(2019-03-07)
Chou, Po-Hao
;
Liao, Wei-Chao
;
Tsai, Kuo-Wang
;
Chen, Ku-Chung
;
Yu, Jau-Song
Because of innumerable cancer sequencing projects, abundant transcriptome expression profiles together with survival data are available from the same patients. Although some expression signatures for prognosis or pathologic staging have been identified from these data, systematically discovering such kind of expression signatures remains a challenge. To address this, we developed TACCO (Transcriptome Alterations in CanCer Omnibus), a database for identifying differentially expressed genes and altered pathways in cancer. TACCO also reveals miRNA cooperative regulations and supports construction of models for prognosis. The resulting signatures have great potential for patient stratification and treatment decision-making in future clinical applications. TACCO is freely available at http://tacco.life.nctu.edu.tw/.
Tunable topological semimetallic phases in Kondo lattice systems
(2019-01-22)
Lu, Yen-Wen
;
Chou, Po-Hao
;
Chung, Chung-Hou
;
Mou, Chung-Yu
;
電子物理學系
We exploit topological semimetallic phases resulting from the Kondo screening in Anderson lattice models. It is shown that by including spin-orbit interactions both in the bulk electrons and in the hybridization between the conduction electrons and electrons in the f orbit, all types of topological semimetallic phases can be realized in Anderson lattice models. Specifically, upon either broken time-reversal symmetry or broken inversion symmetry, we find that either the Weyl semimetallic phase, Dirac semimetallic phase, or nodal-ring semimetallic phases always emerge between insulating phases and can be accessed by tuning either temperature or spin-orbit interaction. For Anderson lattice models with general three-dimensional spin-orbit hybridization between the conduction electrons and electrons in the f orbit, we find that Weyl nodal-ring semimetallic phases emerge between strong and weak topological insulating phases. Furthermore, in the presence of an exchange field, Weyl semimetallic phases form after two Weyl points of charge +/- 1 split off from a Dirac point at time-reversal momenta. On the other hand, when the spin-orbit interaction is included in the conduction electron, we find that upon the rotation symmetry being broken with anisotropic hopping amplitudes, a Weyl semimetallic phase emerges with a double Weyl node with charges of +/- 2. Furthermore, the Weyl semimetallic phases with charges of +/- 2 can be tuned into Weyl semimetallic phases with charges of +/- 1 through the inclusion of the Rashba spin-orbit interaction. Our analyses indicate that Anderson lattices with appropriate spin-orbit interactions provide a platform for realizing all types of topological semimetallic phases.