arXiv subjects

Kent R. Shirer

Publications and source records attributed to Kent R. Shirer.

6 recordsLinked to original sources

arXiv2026

Frequency-modulated enhancement of microwave resonator sensing

We use the Pound-Drever-Hall (PDH) technique to characterize the frequency stability of a microwave-frequency surface acoustic wave (SAW) resonator-based sensor. The multi-mode acoustic resonator is integrated in a notch geometry with a transmission line, all fabricated on Y-cut lithium niobate. We measure the amplitude and phase of the resonator transfer function and the PDH signal across the resonator full spectral range. We use these measurements to emphasize the differences between the PDH measurement and a standard Phase-Locked Loop (PLL) technique. As compared to a PLL, we demonstrate that PDH is insensitive to phase error and exhibits a reduced Allan deviation of the center frequency measurement, in each case by up to an order of magnitude. The method rejects spurious effects and background frequency drift, demonstrating the enhancements possible with PDH-based measurements, which can be realized in a wide range of microwave-frequency resonator-based sensors and devices.

physics.app-ph↗

arXiv2023

Reply to: Low-frequency quantum oscillations in LaRhIn$_5$: Dirac point or nodal line?

We thank G.P. Mikitik and Yu.V. Sharlai for contributing this note and the cordial exchange about it. First and foremost, we note that the aim of our paper is to report a methodology to diagnose topological (semi)metals using magnetic quantum oscillations. Thus far, such diagnosis has been based on the phase offset of quantum oscillations, which is extracted from a "Landau fan plot". A thorough analysis of the Onsager-Lifshitz-Roth quantization rules has shown that the famous $π$-phase shift can equally well arise from orbital- or spin magnetic moments in topologically trivial systems with strong spin-orbit coupling or small effective masses. Therefore, the "Landau fan plot" does not by itself constitute a proof of a topologically nontrivial Fermi surface. In the paper at hand, we report an improved analysis method that exploits the strong energy-dependence of the effective mass in linearly dispersing bands. This leads to a characteristic temperature dependence of the oscillation frequency which is a strong indicator of nontrivial topology, even for multi-band metals with complex Fermi surfaces. Three materials, Cd$_3$As$_2$, Bi$_2$O$_2$Se and LaRhIn$_5$ served as test cases for this method. Linear band dispersions were detected for Cd$_3$As$_2$, as well as the $F$ $\approx$ 7 T pocket in LaRhIn$_5$.

cond-mat.str-el↗

arXiv2022

Temperature dependence of quantum oscillations from non-parabolic dispersions

The phase offset of quantum oscillations is commonly used to experimentally diagnose topologically non-trivial Fermi surfaces. This methodology, however, is inconclusive for spin-orbit-coupled metals where $π$-phase-shifts can also arise from non-topological origins. Here, we show that the linear dispersion in topological metals leads to a $T^2$-temperature correction to the oscillation frequency that is absent for parabolic dispersions. We confirm this effect experimentally in the Dirac semi-metal Cd$_3$As$_2$ and the multiband Dirac metal LaRhIn$_5$. Both materials match a tuning-parameter-free theoretical prediction, emphasizing their unified origin. For topologically trivial Bi$_2$O$_2$Se, no frequency shift associated to linear bands is observed as expected. However, the $π$-phase shift in Bi$_2$O$_2$Se would lead to a false positive in a Landau-fan plot analysis. Our frequency-focused methodology does not require any input from ab-initio calculations, and hence is promising for identifying correlated topological materials.

cond-mat.str-el↗

arXiv2020

Non-monotonic pressure dependence of high-field nematicity and magnetism in CeRhIn$_5$

CeRhIn$_5$ provides a textbook example of quantum criticality in a heavy fermion system: Pressure suppresses local-moment antiferromagnetic (AFM) order and induces superconductivity in a dome around the associated quantum critical point (QCP) near $p_{c} \approx 23\,$kbar. Strong magnetic fields also suppress the AFM order at a field-induced QCP at $B_{\rm c}\approx 50\,$T. In its vicinity, a nematic phase at $B^*\approx 28\,$T characterized by a large in-plane resistivity anisotropy emerges. Here, we directly investigate the interrelation between these phenomena via magnetoresistivity measurements under high pressure. As pressure increases, the nematic transition shifts to higher fields, until it vanishes just below $p_{\rm c}$. While pressure suppresses magnetic order in zero field as $p_{\rm c}$ is approached, we find magnetism to strengthen under strong magnetic fields due to suppression of the Kondo effect. We reveal a strongly non-mean-field-like phase diagram, much richer than the common local-moment description of CeRhIn$_5$ would suggest.

cond-mat.str-el↗

arXiv2020

A new stress dilatometer and measurement of the thermal expansion under uniaxial stress of Mn$_3$Sn

We present a method for measuring thermal expansion under tunable uniaxial stresses, and show measurements of the thermal expansion of Mn$_3$Sn, a room temperature antiferromagnet that exhibits a spontaneous Hall effect, under uniaxial stresses of up to 1.51 GPa compression. Measurement of thermal expansion provides thermodynamic data about the nature of phase transitions, and uniaxial stress provides a powerful tuning method that does not introduce disorder. Mn$_3$Sn exhibits an anomaly in its thermal expansion near $\sim$270 K, associated with a first-order change in its magnetic structure. We show this transition temperature is suppressed by 54.6 K by 1.51 GPa compression along [0001]. We find the associated entropy change at the transition to be $\sim$ 0.1 J mol$^{-1}$ K$^{-1}$ and to vary only weakly with applied stress.

cond-mat.str-el↗

arXiv2018

Dirac fermions in the heavy-fermion superconductors Ce(Co,Rh,Ir)In$_5$

The Ce(Co,Rh,Ir)In$_5$ family of ``Ce-115'' materials hosts an abundance of correlated electron behavior, including heavy-fermion physics, magnetism, superconductivity and nematicity. The complicated behavior of these entangled phenomena leads to a variety of exotic physical properties, which, despite the seemingly simple crystal structure of these compounds, remain poorly understood. It is generally accepted that the interplay between the itinerant and local character of Ce-$4f$ electrons is the key to their exotic behavior. Here, we report theoretical evidence that the Ce-115 materials are also topological semi-metals, with Dirac fermions around well-separated nodes. Dirac nodes in each compound are present on the $Γ-Z$ plane close to the Fermi level. As the Dirac bands are derived from In-orbitals, they occur in all family members irrespective of the transition metal (Co,Rh,Ir). We present the expected Fermi-arc surface state patterns and show the close proximity of a topological Lifshitz transition, which possibly explains the high field physics of Ce-115 materials. Experimentally, we highlight the surprising similarity of Ce(Co,Rh,Ir)In$_5$ in high magnetic fields, despite the distinctly different states of the Ce-$4f$ electrons. These results raise questions about the role Dirac fermions play in exotic transport behavior, and we propose this class of materials as a prime candidate for unconventional topological superconductivity.

cond-mat.str-el↗