Carrier-stabilized hexagonal Ge

Cai, Xuefen; Deng, Hui‐Xiong; Wei, Su‐Huai

doi:10.1103/physrevb.103.245202

Cited by 12 publications

(17 citation statements)

References 31 publications

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“…The effect of doping is, of course, relevant for the transport properties and we want to consider it in the following. It is also expected that doping can play a role in stabilizing the hexago- nal phase, as suggested by calculations for 𝑛-doped Ge [54].…”

Section: Carrier Densitiesmentioning

confidence: 83%

Ensemble averages of ab initio optical, transport, and thermoelectric properties of hexagonal Si$_x$Ge$_{1-x}$ alloys

Borlido¹,

Bechstedt²,

Botti³

et al. 2022

Preprint

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We present a comprehensive first-principles investigation of optical, transport, and thermoelectric properties of pure and doped hexagonal Si 𝑥 Ge 1−𝑥 alloys based on density-functional theory calculations, the Boltzmann transport equation, and the generalized quasi-chemical approximation to obtain alloy averages of electronic properties. At low temperature, phase decomposition into the hexagonal elementary crystals is thermodynamically favored, but around and above room temperature random alloys are predicted to be stable. While hexagonal Si has an indirect band gap, the gap of hexagonal Ge is direct with very weak optical transitions at the absorption edge. The alloy band gap remains direct for a Si content below 45 % and the oscillator strength of the lowest optical transitions is efficiently enhanced by alloying. The optical spectra show clear trends and both absorption edges and prominent peaks can be tuned with composition. The dependence of transport coefficients on carrier concentration and temperature is similar in cubic and hexagonal alloys. However, the latter display anisotropic response due to the reduced hexagonal symmetry. In particular, the transport mass exhibits a significant directional dependence. Seebeck coefficients and thermoelectric power factors of 𝑛-doped alloys show non-monotonous variations with the Si content independently of temperature.

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Section: Carrier Densitiesmentioning

confidence: 83%

Ensemble averages of ab initio optical, transport, and thermoelectric properties of hexagonal Si$_x$Ge$_{1-x}$ alloys

Borlido¹,

Bechstedt²,

Botti³

et al. 2022

Preprint

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show abstract

“…Increasing the degree of non-Hermiticity also can drive the system into the critical phase, and then into the topological trivial Anderson localized phase, when the disorder strength is finite. The model can map to a system of two coupled non-Hermitian AAH chains [63], which can be experimentally realized in electric circuits [26,44,79,80].…”

Section: Discussionmentioning

confidence: 99%

“…When h = 0, the Hermitian disordered Kitaev chain is obtained [63,64], in which topological and AL phase transitions are well studied. When ∆ = 0, the model reduces to the non-Hermitian AAH model [26,44]. It undergoes a non-Hermitian topological phase transition, where the spectrum changes from real to complex with loops, and accompanied by the AL phase transition.…”

Section: Model Symmetries and Phase Diagrammentioning

confidence: 99%

“…To study the topology of spectrum, we introduce an additional dimension by adding a phase δ in the complex quasiperiodic potential. Given V j = 2V cos(2πβj + ih + δ/L), winding numbers of energy spectra are defined as [26,44]…”

Section: Pt Symmetry Breaking and Winding Numbers Of Spectrummentioning

confidence: 99%

“…Besides, non-Hermitian quasiperiodic systems, such as various extensions of the AAH model, have also been intensively studied very recently. The interplay between skin effect and quasiperiodicity leads to asymmetrical AL, and boundary-dependent topologies and self-dualities [26][27][28]. Complex quasiperiodic potentials result in PT symmetry breaking, topological phase transitions, mobility edges, modified ALs and topological Anderson insulators [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43].…”

Section: Introductionmentioning

confidence: 99%

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Anderson localization and topological phase transitions in non-Hermitian Aubry-André-Harper models with p-wave pairing

Cai

2021

Preprint

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We study non-Hermitian Aubry-André-Harper models with p-wave pairing, where the non-Hermiticity is introduced by on-site complex quasiperiodic potentials. By analysing the PT symmetry breaking, winding numbers of energy spectra, localization and fractal dimensions of states, and fate of Majorana fermions, a complete phase diagram on Anderson localization and topological phase transitions is obtained. In particular, the non-Hermitian topological nature of Anderson localization phase transitions from extended to critical and then to localized phases is identified, using both analytical and numerical methods. In the critical phase the complex spectrum is topological nontrivial with a fractional winding number. In the localized phase the analytical localization length of states can apply to the Hermitian case, which is absent so far. Both the non-Hermiticity and disorder are detrimental to Majorana fermions.

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Light‐Induced Frenkel Defect Pair Formation Can Lead to Phase‐Segregation of Otherwise Miscible Halide Perovskite Alloys

Sabino,

Dalpian,

Zunger

2023

Advanced Energy Materials

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Alloys of ABX3 halide perovskites (HP) exhibit unique phase behavior compared to traditional III‐V and II‐VI semiconductor alloys used in solar cells. While the latter typically have good mutual miscibility when their mixed components are size matched, and phase‐segregate when size mismatched, HP alloys show good miscibility in the dark but can phase‐segregate under light. Quantum mechanical calculations described herein reveal light‐induced defect formation and migration hold the key. Specifically, the interaction between a halogen vacancy VX with halogen interstitial Xi forming together a Frenkel‐pair defect emerges as the enabler for phase‐segregation in HP alloys. At a threshold bromine composition in the Br‐I alloys, the photogenerated holes in the valence band localize, creating thereby a doubly‐charged iodine Frenkel‐pair (VI + Ii)2+. Faster migration of iodine over bromine interstitial into the vacant iodine VI site leads to the formation of iodine‐rich and iodine‐depleted regions, establishing phase‐segregation. Removal of the mobile defects–the agent of segregation–by dark thermal annealing, supplies the opposing force, leading to reversal of phase‐segregation. This atomistic understanding can enable some control of the phase‐segregation by selecting substituting elements on the B site–such as replacing some Pb by Sn–that are unable to form stable Frenkel defects.

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Carrier-stabilized hexagonal Ge

Cited by 12 publications

References 31 publications

Ensemble averages of ab initio optical, transport, and thermoelectric properties of hexagonal Si$_x$Ge$_{1-x}$ alloys

Ensemble averages of ab initio optical, transport, and thermoelectric properties of hexagonal Si$_x$Ge$_{1-x}$ alloys

Anderson localization and topological phase transitions in non-Hermitian Aubry-André-Harper models with p-wave pairing

Light‐Induced Frenkel Defect Pair Formation Can Lead to Phase‐Segregation of Otherwise Miscible Halide Perovskite Alloys

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