Abstract-High-frequency breakdown of the integer QHE in GaAs/AlGaAs heterojunctions

V. Dziom, A. Shuvaev, A. V. Shchepetilnikov, D. MacFarland, G. Strasser, A. Pimenov

https://arxiv.org/abs/1811.08777

The integer quantum Hall effect is a well-studied phenomenon at frequencies below about 100 Hz. The plateaus in high-frequency Hall conductivity were experimentally proven to retain up to 33 GHz, but the behavior at higher frequencies has remained largely unexplored. Using continuous wave THz spectroscopy, the complex Hall conductivity of GaAs/AlGaAs heterojunctions was studied in the range of 69-1100 GHz. Above 100 GHz, the quantum plateaus are strongly smeared out and replaced by weak quantum oscillations in the real part of the conductivity. The amplitude of the oscillations decreases with increasing frequency. Near 1 THz, the Hall conductivity does not reveal any features related to the filling of Landau levels. Similar oscillations are observed in the imaginary part as well, this effect has no analogy at zero frequency. This experimental picture is in disagreement with existing theoretical considerations of the high-frequency quantum Hall effect.

Abstract-Electric field control of terahertz polarization in a multiferroic manganite with electromagnons

A. Shuvaev, V. Dziom, Anna Pimenov, M. Schiebl, A. A. Mukhin, A. Komarek, T. Finger, M. Braden, A. Pimenov

(Submitted on 5 Apr 2017)

https://arxiv.org/abs/1704.01498

All-electrical control of a dynamic magnetoelectric effect is demonstrated in a classical multiferroic manganite DyMnO3, a material containing coupled antiferromagnetic and ferroelectric orders. Due to intrinsic magnetoelectric coupling with electromagnons a linearly polarized terahertz light rotates upon passing through the sample. The amplitude and the direction of the polarization rotation are defined by the orientation of ferroelectric domains and can be switched by static voltage. These experiments allow the terahertz polarization to be tuned using the dynamic magnetoelectric effect.

Abstract-Terahertz spectroscopy of crystal-field transitions in magnetoelectric TmAl3(BO3)4

A. M. Kuzmenko, A. A. Mukhin, V. Vu. Ivanov, G. A. Komandin, A. Shuvaev, A. Pimenov, V. Dziom, L. N. Bezmaternykh, I. A. Gudim

(Submitted on 7 Apr 2017)

https://arxiv.org/abs/1704.02198

Dynamic magnetic properties of magnetoelectric TmAl3(BO3)4 borate have been investigated by terahertz spectroscopy. Crystal field (CF) transitions within the ground multiplet 3H6 of Tm3+ ions are observed and they are identified as magnetic-dipole transitions from the ground singlet A1 to the next excited doublet E of Tm3+ ions. Unexpected fine structure of the transitions is detected at low temperatures. The new modes are assigned to local distortions of the sites with D3 symmetry by Bi3+ impurities, which resulted in the splitting of A1 -> E transition. Two types of locally distorted sites are identified and investigated. The main contribution to the static magnetic susceptibility is shown to be determined by the matrix elements of the observed magnetic transitions. We demonstrate that even in case of local distortions the symmetry of the undistorted crystal is recovered for magnetic and for quadratic magnetoelectric susceptibilities.

Abstract-Terahertz properties of Dirac fermions in HgTe films with optical doping

V. Dziom, A. Shuvaev, N. N. Mikhailov, A. Pimenov

http://arxiv.org/abs/1603.05926

Terahertz properties of mercury telluride (HgTe) films with critical thickness are presented and discussed. The density of the charge carriers is controlled using contact-free optical doping by visible light. In the magneto-optical response of HgTe the contribution of two types of carriers (electrons and holes) can be identified. The density of the electrons can be modified by light illumination by more than one order of magnitude. As the hole density is roughly illuminationindependent, the terahertz response of the illuminated samples becomes purely electronic. In some cases, light illumination may switch the qualitative electrodynamic response from hole-like to the electron-like. The cyclotron mass of the electrons could be extracted from the data and shows a square root dependence upon the charge concentration in the broad range of parameters. This can be interpreted as a clear proof of a linear dispersion relations, i.e. Dirac-type charge carriers.