Latest Papers in Condensed Matter Physics

Mesoscale And Nanoscale Physics

---

On intrinsic Stokes shift in wide GaN/AlGaN polar quantum wells (1903.04481v1)

M. Jarema, M. Gladysiewicz, E. Zdanowicz, E. Bellet-Amalric, E. Monroy, R. Kudrawiec

2019-03-11

The interpretation of electromodulated reflectance (ER) spectra of polar quantum wells (QWs) is difficult even for homogeneous structures because of the built-in electric field. In this work we compare the room-temperature contactless ER and photoluminescence (PL) spectra of polar GaN/AlGaN QWs with the effective-mass band structure calculations. We show that the emission from the ground state transition is observed in PL but the ER is dominated by transitions between excited states. This effect results from the polarization-induced built-in electric field in QW that breaks the selection rules that apply to square-like QWs, allowing many optical transitions which cannot be separately distinguished in the ER spectrum. We develop the guidelines for the identification of optical transitions observed in PL and ER spectra. We conclude that an intrinsic Stokes shift, i.e., a shift between emission and absorption, is present even for homogeneous GaN/AlGaN QWs with large width, where the electron-hole wavefunction overlap for the fundamental transition is weak.

A coherent nanomechanical oscillator driven by single-electron tunnelling (1903.04474v1)

Yutian Wen, N. Ares, F. J. Schupp, T. Pei, G. A. D. Briggs, E. A. Laird

2019-03-11

A single-electron transistor incorporated as part of a nanomechanical resonator represents an extreme limit of electron-phonon coupling. While it allows for fast and sensitive electromechanical measurements, it also introduces backaction forces from electron tunnelling which randomly perturb the mechanical state. Despite the stochastic nature of this backaction, under conditions of strong coupling it is predicted to create self-sustaining coherent mechanical oscillations. Here, we verify this prediction using time-resolved measurements of a vibrating carbon nanotube transistor. This electromechanical oscillator has intriguing similarities with a laser. The single-electron transistor, pumped by an electrical bias, acts as a gain medium while the resonator acts as a phonon cavity. Despite the unconventional operating principle, which does not involve stimulated emission, we confirm that the output is coherent, and demonstrate other laser behaviour including injection locking and frequency narrowing through feedback.

Bayesian estimation for quantum sensing in the absence of single-shot detection (1806.01249v3)

Hossein T. Dinani, Dominic W. Berry, Raul Gonzalez, Jeronimo R. Maze, Cristian Bonato

2018-06-04

Quantum information protocols, such as quantum error correction and quantum phase estimation, have been widely used to enhance the performance of quantum sensors. While these protocols have relied on single-shot detection, in most practical applications only an averaged readout is available, as in the case of room-temperature sensing with the electron spin associated with a nitrogen-vacancy center in diamond. Here, we theoretically investigate the application of the quantum phase estimation algorithm for high dynamic-range magnetometry, in the case where single-shot readout is not available. We show that, even in this case, Bayesian estimation provides a natural way to use the available information in an efficient way. We apply Bayesian analysis to achieve an optimized sensing protocol for estimating a time-independent magnetic field with a single electron spin associated to a nitrogen-vacancy center at room temperature and show that this protocol improves the sensitivity over previous protocols by more than a factor of 3. Moreover, we show that an extra enhancement can be achieved by considering the timing information in the detector clicks.

Topology in abundance (1903.00564v2)

Étienne Lantagne-Hurtubise, Marcel Franz

2019-03-01

The topological classification of all known non-magnetic crystalline compounds is now complete, revealing thousands of new candidate topological materials waiting to be explored in the lab.

Unconventional gate voltage dependence of the charge conductance caused by spin-splitting Fermi surface by Rashba-type spin-orbit coupling (1903.04346v1)

D. Oshima, K. Taguchi, Y. Tanaka

2019-03-11

We calculate the gate voltage (Vg) dependence of charge conductance in a normal metal (NM)/two dimensional electron gas (2DEG) junction, where Rashba spin-orbit coupling and ferromagnetism exist in the 2DEG. We call this 2DEG as the ferromagnetic Rashba metal (FRM) and the chemical potential of the FRM is controlled by Vg. We clarify the physical origin of the unconventional Vg dependence of charge conductance in the NM/FRM junction found in our previous work [J. Phys. Soc. Jpn. 87, 034710 (2018)], in which the charge conductance increases with Vg, although the number of carries in FRM decreases. We calculate the momentum-resolved charge conductance. It is clarified that the origin of the unconventional Vg dependence is due to the non-monotonic change in the size of the inner Fermi surface in FRM as a function of .

---

Thank you for reading!

Don't forget to Follow and Resteem. @arxivsanity
Keeping everyone inform.