arXiv subjects

V. P. Dravid

Publications and source records attributed to V. P. Dravid.

5 recordsLinked to original sources

arXiv2025

Comparison of Nb and Ta Pentoxide Loss Tangents for Superconducting Quantum Devices

Superconducting transmon qubits are commonly made with thin-film Nb wiring, but recent studies have shown increased performance with Ta wiring. In this work, we compare the resonator-induced single photon, millikelvin dielectric loss for pentoxides of Nb (Nb2O5) and Ta (Ta2O5) in order to further understand limiting losses in qubits. Nb and Ta pentoxides of three thicknesses are deposited via pulsed laser deposition onto identical coplanar waveguide resonators. The two-level system (TLS) loss in Nb2O5 is determined to be about 30% higher than that of Ta2O5. This work indicates that qubits with Nb wiring are affected by higher loss arising from the native pentoxide itself, likely in addition to the presence of suboxides, which are largely absent in Ta.

quant-ph↗

arXiv2015

Two Band Model Interpretation of the p to n Transition in Ternary Tetradymite Topological Insulators

The requirement for large bulk resistivity in topological insulators has led to the design of complex ternary and quaternary phases with balanced donor and acceptor levels. A common feature of the optimized phases is that they lie close to the p to n transition. The tetradymite Bi2Te3_xSex system exhibits minimum bulk conductance at the ordered composition Bi2Te2Se. By combining local and integral measurements of the density of states, we find that the point of minimum electrical conductivity at x=1.0 where carriers change from hole-like to electron-like is characterized by conductivity of the mixed type. Our experimental findings, which are interpreted within the framework of a two band model for the different carrier types, indicate that the mixed state originates from different type of native defects that strongly compensate at the crossover point.

cond-mat.mtrl-sci↗

arXiv2004

Ultraviolet photonic crystal laser

We fabricated two dimensional photonic crystal structures in zinc oxide films with focused ion beam etching. Lasing is realized in the near ultraviolet frequency at room temperature under optical pumping. From the measurement of lasing frequency and spatial profile of the lasing modes, as well as the photonic band structure calculation, we conclude that lasing occurs in the strongly localized defect modes near the edges of photonic band gap. These defect modes originate from the structure disorder unintentionally introduced during the fabrication process.

physics.optics↗

arXiv2003

Origin of room temperature ferromagnetism in homogeneous (In,Mn)As thin films

The microstructure of (In,Mn)As thin films grown using metalorganic vapor phase epitaxy (MOVPE) was investigated to determine the origin of room temperature ferromagnetism in these films. Transmission electron microscopy (TEM) based techniques were used to investigate phase purity and compositional homogeneity. Microanalysis of an In1-xMnxAs film with x = 0.01 and a Curie temperature of 330 K exhibited a homogeneous distribution of Mn. High Mn concentration films with x = 0.20 exhibited MnAs precipitates within the (In,Mn)As matrix. The analysis indicates that room temperature ferromagnetic, single-phase (In,Mn)As can be formed by MOVPE. The origin of ferromagnetism is attributed to (In,Mn)As solid solution rather than distinct secondary Mn-rich magnetic phase(s).

cond-mat.mtrl-sci↗

arXiv1996

Momentum-Dependent Charge Transfer Excitations in Sr2CuO2Cl2 - Angle Resolved Electron Energy Loss Spectroscopy

Electron-hole pair excitations in the insulating cuprates $Sr_2CuO_2Cl_2$ were investigated by angle-resolved electron energy loss spectroscopy. The optically allowed and optically forbidden transitions were observed to be strongly anisotropic in $Cu-O_2$ plane. The former show a large energy dispersion $\sim 1.5$eV along [110], and the latter appear at a higher energy position ($\sim 4.5$eV) only along [100], but not along [110]. We interpret these results as transitions involving excitons. A small exciton model is examined to explain both the observed features.

cond-mat↗