arXiv subjects

P. Vogt

Publications and source records attributed to P. Vogt.

4 recordsLinked to original sources

arXiv2023

Growth of $α-Ga_2O_3$ on $Al_2O_3$ by conventional molecular-beam epitaxy and metal-oxide-catalyzed epitaxy

We report the growth of $α-Ga_2O_3$ on $m$-plane $Al_2O_3$ by conventional plasma-assisted molecular-beam epitaxy (MBE) and In-mediated metal-oxide-catalyzed epitaxy (MOCATAXY). We report a growth-rate-diagram for $α-Ga_2O_3$ (10-10), and observe (i) a growth rate increase, (ii) an expanded growth window, and (iii) reduced out-of-lane mosaic spread when MOCATAXY is employed for the growth of $α-Ga_2O_3$. Through the use of In-mediated catalysis, growth rates over $0.2\,μ\text{m}\,\text{hr}^{-1}$ and rocking curves with full width at half maxima of $Δω\approx 0.45^{\circ}$ are achieved. Faceting is observed along the $α-Ga_2O_3$ film surface and is explored through scanning transmission electron microscopy.

cond-mat.mtrl-sci↗

arXiv2014

Specific heat of K071Na0.29Fe2As2 at very low temperatures

A commercially available calorimeter has been used to investigate the specific heat of a high-quality \kn\ single crystal. The addenda heat capacity of the calorimeter is determined in the temperature range $0.02 \, \mathrm{K} \leq T \leq 0.54 \, \mathrm{K}$. The data of the \kn\ crystal imply the presence of a large $T^2$ contribution to the specific heat which gives evidence of $d$-wave order parameter symmetry in the superconducting state. To improve the measurements, a novel design for a calorimeter with a paramagnetic temperature sensor is presented. It promises a temperature resolution of $ΔT \approx 0.1 \, \mathrm{μK}$ and an addenda heat capacity less than $200 \, \mathrm{pJ/K}$ at $ T < 100 \, \mathrm{mK}$.

cond-mat.supr-con↗

arXiv2013

Evidence of d-wave Superconductivity in K_(1-x)Na_xFe_2As_2 (x = 0, 0.1) Single Crystals from Low-Temperature Specific Heat Measurements

From the measurement and analysis of the specific heat of high-quality K_(1-x)Na_xFe_2As_2 single crystals we establish the presence of large T^2 contributions with coefficients alpha_sc ~ 30 mJ/mol K^3 at low-T for both x=0 and 0.1. Together with the observed square root field behavior of the specific heat in the superconducting state both findings evidence d-wave superconductivity on almost all Fermi surface sheets with an average gap amplitude of Delta_0 in the range of 0.4 - 0.8 meV. The derived Delta_0 and the observed T_c agree well with the values calculated within the Eliashberg theory, adopting a spin-fluctuation mediated pairing in the intermediate coupling regime.

cond-mat.supr-con↗

arXiv1999

Photon production in heavy-ion collisions close to the pion threshold

We report on a measurement of hard photons (Eg>30 MeV) in the reaction Ar+Ca at 180A MeV at an energy in which photons from the decay of pi0 mesons are dominating. Simultaneous measurement with the TAPS spectrometer of the photon spectrum and photon-photon coincidences used for the identification of pi0 enabled the subtraction of pi0 contribution. The resulting photon spectrum exhibits an exponential shape with an inverse slope of E0=(53+-0.03(stat)-5+8(syst)) MeV. The photon multiplicity, equal to (1.21+-0.03(stat)+0.3-0.2(syst))10E0-2, is roughly one order of magnitude larger than the value extrapolated from existing systematics. This enhancement of the hard photon production is attributed to a strong increase in the contribution of secondary np collisions to the total photon yield. We conclude that, on average, the number of np collisions which contribute to the hard photon production is 7 times larger than the number of first chance np collisions in the reaction Ar+Ca at 180A MeV.

nucl-ex↗