arXiv subjects

Susumu Takahashi

Publications and source records attributed to Susumu Takahashi.

29 records · Page 2Linked to original sources

arXiv2016

Measurement of paramagnetic spin concentration in a solid-state system using double electron-electron resonance

Diamond has been extensively investigated recently due to a wide range of potential applications of nitrogen-vacancy (NV) defect centers existing in a diamond lattice. The applications include magnetometry and quantum information technologies, and long decoherence time ($T_2$) of NV centers is critical for those applications. Although it has been known that $T_2$ highly depends on the concentration of paramagnetic impurities in diamond, precise measurement of the impurity concentration remains challenging. In the preset work, we show a method to determine a wide range of the nitrogen concentration ($n$) in diamond using a wide-band high-frequency electron spin resonance and double electron-electron resonance spectrometer. Moreover, we investigate $T_2$ of the nitrogen impurities and show the relationship between $T_2$ and $n$. The method developed here is applicable for various spin systems in solid and implementable in nanoscale magnetic resonance spectroscopy with NV centers to characterize the concentration of the paramagnetic spins within a microscopic volume.

cond-mat.mes-hall↗

arXiv2015

High-frequency and high-field optically detected magnetic resonance of nitrogen-vacancy centers in diamond

We present the development of an optically detected magnetic resonance (ODMR) system, which enables us to perform the ODMR measurements of a single defect in solids at high frequencies and high magnetic fields. Using the high-frequency and high-field ODMR system, we demonstrate 115 GHz continuous-wave and pulsed ODMR measurements of a single nitrogen-vacancy (NV) center in a diamond crystal at the magnetic field of 4.2 Tesla as well as investigation of field dependence ($0-8$ Tesla) of the longitudinal relaxation time ($T_1$) of NV centers in nanodiamonds.

cond-mat.mes-hall↗

arXiv2014

A high-frequency electron paramagnetic resonance spectrometer for multi-dimensional, -frequency and -phase pulsed measurements

We describe instrumentation for a high-frequency electron paramagnetic resonance (EPR) and pulsed electron-electron double resonance (PELDOR) spectroscopy. The instrumentation is operated in the frequency range of 107$-$120 GHz and 215$-$240 GHz and in the magnetic field range of 0$-$12.1 Tesla. The spectrometer consisting of a high-frequency high-power solid-state source, a quasioptical system, a phase-sensitive detection system, a cryogenic-free superconducting magnet and a $^4$He cryostat enables multi-frequency continuous-wave EPR spectroscopy as well as pulsed EPR measurements with a few hundred nanosecond pulses. Here we discuss the details of the design and the pulsed EPR sensitivity of the instrumentation. We also present performance of the instrumentation in unique experiments including PELDOR spectroscopy to probe correlations in an insulating electronic spin system and application of dynamical decoupling techniques to extend spin coherence of electron spins in an insulating solid-state system.

physics.ins-det↗

arXiv2012

Spin decoherence and electron spin bath noise of a nitrogen-vacancy center in diamond

We theoretically investigate spin decoherence of a single nitrogen-vacancy (NV) center in diamond. Using the spin coherent state P-representation method, coherence evolution of the NV center surrounded by nitrogen electron spins (N) is simulated. We find that spin decoherence time as well as free-induction decay of the NV center depend on the spatial configuration of N spins. Both the spin decoherence rate (1/T2) and dephasing rate (1/T2*) of the NV center increase linearly with the concentration of the N spins. Using the P-representation method, we also demonstrate extracting noise spectrum of the N spin bath, which will provide promising pathways for designing an optimum pulse sequence to suppress the decoherence in diamond.

quant-ph↗

arXiv2009

Cavity dumping of an injection-locked free-electron laser

This letter reports cavity dumping of an electrostatic-accelerator-driven free-electron laser (FEL) while it is injection-locked to a frequency-stabilized 240 GHz solid-state source. Cavity dumping enhances the FEL output power by a factor of $\sim$8, and abruptly cuts off the end of the FEL pulse. The cavity-dumped, injection-locked FEL output is used in a 240 GHz pulsed electron spin resonance (ESR) experiment.

cond-mat.other↗

arXiv2008

Coherent Manipulation and Decoherence of S=10 Single-Molecule Magnets

We report coherent manipulation of S=10 Fe$_{8}$ single-molecule magnets. The temperature dependence of the spin decoherence time $T_2$ measured by high frequency pulsed electron paramagnetic resonance indicates that strong spin decoherence is dominated by Fe$_{8}$ spin bath fluctuations. By polarizing the spin bath in Fe$_{8}$ single-molecule magnets at magnetic field $B$ = 4.6 T and temperature $T$ = 1.3 K, spin decoherence is significantly suppressed and extends the spin decoherence time $T_2$ to as long as 712 ns. A second decoherence source is likely due to fluctuations of the nuclear spin bath. This hints that the spin decoherence time can be further extended via isotopic substitution to smaller magnetic moments.

cond-mat.mes-hall↗

arXiv2008

Quenching Spin Decoherence in Diamond through Spin Bath Polarization

We experimentally demonstrate that the decoherence of a spin by a spin bath can be completely eliminated by fully polarizing the spin bath. We use electron paramagnetic resonance at 240 gigahertz and 8 Tesla to study the spin coherence time $T_2$ of nitrogen-vacancy centers and nitrogen impurities in diamond from room temperature down to 1.3 K. A sharp increase of $T_2$ is observed below the Zeeman energy (11.5 K). The data are well described by a suppression of the flip-flop induced spin bath fluctuations due to thermal spin polarization. $T_2$ saturates at $\sim 250 μs$ below 2 K, where the spin bath polarization is 99.4 %.

quant-ph↗

arXiv2007

Sub-MHz Linewidth at 240 GHz from an Injection-Locked Free-Electron Laser

Radiation from an ultra-stable 240 GHz solid-state source has been injected, through an isolator, into the cavity of the University of California Santa Barbara (UCSB) MM-wave free-electron laser (FEL). High-power FEL emission, normally distributed among many of the cavity's longitudinal modes, is concentrated into the single mode to which the solid state source has been tuned. The linewidth of the FEL emission is 0.5 MHz, consistent with the Fourier transform limit for the 2 microsecond pulses. This demonstration of frequency-stable, ultra-narrow-band FEL emission is a critical milestone on the road to FEL-based pulsed electron paramagnetic resonance spectroscopy.

cond-mat.other↗

arXiv2006

Microwave spectroscopy of Q1D and Q2D organic conductors

This chapter reviews recent experimental studies of a novel open-orbit magnetic resonance phenomenon. The technique involves measurement of angle-dependent microwave magneto-conductivity and is, thus, closely related to the cyclotron resonance and angle-dependent magnetoresistance techniques. Data for three contrasting materials are presented: (TMTSF)2ClO4, alpha-(BEDT-TTF)2KHg(SCN)4 and kappa-(BEDT-TTF)2I3. These studies reveal important insights into the Fermiology of these novel materials, as well as providing access to important electronic parameters such as the in-plane Fermi velocity and quasiparticle scattering rate. It is argued that all three compounds exhibit coherent three-dimensional band transport at liquid helium temperatures, and that their low-energy magnetoelectrodynamic properties appear to be well explained on the basis of a conventional semiclassical Boltzmann approach. It is also suggested that this technique could be used to probe quasiparticles in nodal superconductors.

cond-mat.supr-con↗

arXiv2005

A rotating cavity for high-field angle-dependent microwave spectroscopy of low-dimensional conductors and magnets

The cavity perturbation technique is an extremely powerful method for measuring the electrodynamic response of a material in the millimeter- and sub-millimeter spectral range (10 GHz to 1 THz), particularly in the case of high-field/frequency magnetic resonance spectroscopy. However, the application of such techniques within the limited space of a high-field magnet presents significant technical challenges. We describe a 7.62 mm x 7.62 mm (diameter x length) rotating cylindrical cavity which overcomes these problems.

cond-mat.other↗

arXiv2003

Structure in the early afterglow lightcurve of the gamma-ray burst of 29 March 2003

Gamma-ray bursts (GRBs) are energetic explosions that for 0.01--100 s are the brightest gamma-ray sources in the sky. Observations of the early evolution of afterglows we expected to provide clues about the nature of the bursts, but their rapid fading has hampered such studies; some recent rapid localizations of bursts have improved the situation. Here we report on an early detection of the very bright afterglow of the burst of 29 March 2003 (GRB030329). Our data show that, even early in the aferglow phase, the light curve shows unexpectedly complicated structures superimposed on the fading background.

astro-ph↗