Shining light on electrons in low dimensions

My research focuses on the behavior of electrons (negatively charged particles repelling each other through the Coulomb force) confined in semiconductor crystals. Under special conditions the mutual Coulomb forces among the electrons can create novel emergent states of matter with remarkable properties. In this paper I will emphasize the conceptual framework of this field of research highlighting general phenomena and outstanding issues. The understanding of these novel, highly-correlated electronic states represents an important aspect of nanoscience and it is the basis for the invention of original and innovative practical devices. My research activity aims to achieve this goal

Charger-mediated energy transfer in exactly-solvable models for quantum batteries

We present a systematic analysis and classification of several models of quantum batteries involving different combinations of two level systems and quantum harmonic oscillators. In particular, we study energy transfer processes from a given quantum system, termed charger, to another one, i.e. the proper battery. In this setting, we analyze different figures of merit, including the charging time, the maximum energy transfer, and the average charging power. The role of coupling Hamiltonians which do not preserve the number of local excitations in the charger-battery system is clarified by properly accounting them in the global energy balance of the model.Comment: 11 page

Interplay between disorder and intersubband collective excitations in the two-dimensional electron gas

Intersubband absorption in modulation-doped quantum wells is usually appropriately described as a collective excitation of the confined two-dimensional electron gas. At sufficiently low electron density and low temperatures, however, the in-plane disorder potential is able to damp the collective modes by mixing the intersubband charge-density excitation with single-particle localized modes. Here we show experimental evidence of this transition. The results are analyzed within the framework of the density functional theory and highlight the impact of the interplay between disorder and the collective response of the two-dimensional electron gas in semiconductor heterostructures.Comment: 5 pages, 4 figures, RevTeX. Accepted for publication in Phys. Rev. B (Rapid. Comm.

High-power collective charging of a solid-state quantum battery

Quantum information theorems state that it is possible to exploit collective quantum resources to greatly enhance the charging power of quantum batteries (QBs) made of many identical elementary units. We here present and solve a model of a QB that can be engineered in solid-state architectures. It consists of $N$ two-level systems coupled to a single photonic mode in a cavity. We contrast this collective model ("Dicke QB"), whereby entanglement is genuinely created by the common photonic mode, to the one in which each two-level system is coupled to its own separate cavity mode ("Rabi QB"). By employing exact diagonalization, we demonstrate the emergence of a quantum advantage in the charging power of Dicke QBs, which scales like $\sqrt{N}$ for $N\gg 1$.Comment: 8 pages, 5 figures. Version v2 supersedes version v1 where a technical mistake was done in using the Holstein-Primakoff transformation. The quantum advantage in the maximum charging power discussed in version v1 has been found to be robust. We have also updated the list of author

Photocurrent-based detection of Terahertz radiation in graphene

Graphene is a promising candidate for the development of detectors of Terahertz (THz) radiation. A well-known detection scheme due to Dyakonov and Shur exploits the confinement of plasma waves in a field-effect transistor (FET), whereby a dc photovoltage is generated in response to a THz field. This scheme has already been experimentally studied in a graphene FET [L. Vicarelli et al., Nature Mat. 11, 865 (2012)]. In the quest for devices with a better signal-to-noise ratio, we theoretically investigate a plasma-wave photodetector in which a dc photocurrent is generated in a graphene FET. The rectified current features a peculiar change of sign when the frequency of the incoming radiation matches an even multiple of the fundamental frequency of plasma waves in the FET channel. The noise equivalent power per unit bandwidth of our device is shown to be much smaller than that of a Dyakonov-Shur detector in a wide spectral range.Comment: 5 pages, 4 figure

First-Order Phase Transition in a Quantum Hall Ferromagnet

The single-particle energy spectrum of a two-dimensional electron gas in a perpendicular magnetic field consists of equally-spaced spin-split Landau levels, whose degeneracy is proportional to the magnetic field strength. At integer and particular fractional ratios between the number of electrons and the degeneracy of a Landau level (filling factors n) quantum Hall effects occur, characterised by a vanishingly small longitudinal resistance and quantised Hall voltage. The quantum Hall regime offers unique possibilities for the study of cooperative phenomena in many-particle systems under well-controlled conditions. Among the fields that benefit from quantum-Hall studies is magnetism, which remains poorly understood in conventional material. Both isotropic and anisotropic ferromagnetic ground states have been predicted and few of them have been experimentally studied in quantum Hall samples with different geometries and filling factors. Here we present evidence of first-order phase transitions in n = 2 and 4 quantum Hall states confined to a wide gallium arsenide quantum well. The observed hysteretic behaviour and anomalous temperature dependence in the longitudinal resistivity indicate the occurrence of a transition between the two distinct ground states of an Ising quantum-Hall ferromagnet. Detailed many-body calculations allowed the identification of the microscopic origin of the anisotropy field