About

Karoly Holczer is a Professor in the Department of Physics & Astronomy at UCLA. He holds a Ph.D. from the Central Research Institute for Physics at Roland Eotvos University in Budapest, Hungary, obtained in 1977, and an M.S. from the same university in 1974. His research interests focus on experimental condensed matter physics, specifically organic conductors and superconductors, as well as electron paramagnetic resonance. His work involves investigating the properties of these materials through various experimental techniques, contributing to the understanding of their physical behaviors.

Research topics

• Nuclear magnetic resonance
• Physics
• Materials science
• Chemistry
• Atomic physics
• Condensed matter physics
• Crystallography
• Nuclear physics

Selected publications

• Demonstration of NV-detected $^{13}$C NMR at 4.2 T

  arXiv (Cornell University) · 2023-03-01

  preprintOpen access

  The nitrogen-vacancy (NV) center in diamond has enabled studies of nanoscale nuclear magnetic resonance (NMR) and electron paramagnetic resonance with high sensitivity in small sample volumes. Most NV-detected NMR (NV-NMR) experiments are performed at low magnetic fields. While low fields are useful in many applications, high-field NV-NMR with fine spectral resolution, high signal sensitivity, and the capability to observe a wider range of nuclei is advantageous for surface detection, microfluidic, and condensed matter studies aimed at probing micro- and nanoscale features. However, only a handful of experiments above 1 T were reported. Herein, we report $^{13}$C NV-NMR spectroscopy at 4.2 T, where the NV Larmor frequency is 115 GHz. Using an electron-nuclear double resonance technique, we successfully detect NV-NMR of two diamond samples. The analysis of the NMR linewidth based on the dipolar broadening theory of Van Vleck shows that the observed linewidths from sample 1 are consistent with the intrinsic NMR linewidth of the sample. For sample 2 we find a narrower linewidth of 44 ppm. This work paves the way for new applications of nanoscale NV-NMR.

  PublisherOA PDFDOI

• Demonstration of NV-detected <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi mathvariant="normal">C</mml:mi><mml:mprescripts/><mml:none/><mml:mn>13</mml:mn></mml:mmultiscripts></mml:math> NMR at 4.2 T

  Physical review. B./Physical review. B · 2023-07-26 · 9 citations

  article

  The nitrogen-vacancy (NV) center in diamond has enabled studies of nanoscale nuclear magnetic resonance (NMR) and electron paramagnetic resonance with high sensitivity in small sample volumes. Most NV-detected NMR (NV-NMR) experiments are performed at low magnetic fields. While low fields are useful in many applications, high-field NV-NMR with fine spectral resolution, high signal sensitivity, and the capability to observe a wider range of nuclei is advantageous for surface detection, microfluidic, and condensed matter studies aimed at probing micro- and nanoscale features. However, only a handful of experiments above 1 T were reported. Herein, we report $^{13}\mathrm{C}$ NV-NMR spectroscopy at 4.2 T, where the NV Larmor frequency is 115 GHz. Using an electron-nuclear double resonance technique, we successfully detect NV-NMR of two diamond samples. The analysis of the NMR linewidth based on the dipolar broadening theory of Van Vleck shows that the observed linewidths from sample 1 are consistent with the intrinsic NMR linewidth of the sample. For sample 2 we find a narrower linewidth of 44 ppm. This work paves the way for new applications of nanoscale NV-NMR.

  PublisherDOI

• Ultrahigh nitrogen-vacancy center concentration in diamond

  Carbon · 2021 · 21 citations

  Senior authorCorresponding
  • Materials science
  • Atomic physics
  • Chemistry
  PublisherOA PDFDOI

• Demonstration of NV-detected ESR spectroscopy at 115 GHz and 4.2 T

  Applied Physics Letters · 2020 · 12 citations

  • Atomic physics
  • Materials science
  • Nuclear magnetic resonance

  High frequency electron spin resonance (ESR) spectroscopy is an invaluable tool for identification and characterization of spin systems. Nanoscale ESR using the nitrogen-vacancy (NV) center has been demonstrated down to the level of a single spin. However, NV-detected ESR has exclusively been studied at low magnetic fields, where the spectral overlap prevents clear identification of spectral features. In this work, we demonstrate NV-detected ESR measurements of single-substitutional nitrogen impurities in diamond at a NV Larmor frequency of 115 GHz and the corresponding magnetic field of 4.2 T. The NV-ESR measurements utilize a double electron-electron resonance sequence and are performed using both ensemble and single NV spin systems. In the single NV experiment, chirp pulses are used to improve the population transfer and for NV-ESR measurements. This work provides the basis for NV-based ESR measurements of external spins at high magnetic fields.

  PublisherDOI

• Correction to: Ultrathin Metasurface Wavelength-Selective Mirror for Millimeter/TerahertzWave Fabry-Perot Cavities

  Journal of Infrared Millimeter and Terahertz Waves · 2020-03-05

  articleOpen access
  PublisherOA PDFDOI

• Optical–Microwave Pump–Probe Studies of Electronic Properties in Novel Materials

  physica status solidi (b) · 2020-10-09

  articleOpen access

  Combined microwave–optical pump–probe methods are emerging to study the quantum state of spin qubit centers and the charge dynamics in semiconductors. A major hindrance is the limited bandwidth of microwave irradiation/detection circuitry which can be overcome with the use of broadband coplanar waveguides (CPWs). The development and performance characterization of two spectrometers is presented as follows: an optically detected magnetic resonance spectrometer (ODMR) and a microwave‐detected photoconductivity measurement. In the first method, light serves as detection and microwaves excite the investigated medium, whereas in the second, the roles are interchanged. The performance is demonstrated by measuring ODMR maps on the nitrogen‐vacancy (NV) center in diamond and time‐resolved photoconductivity in p ‐doped silicon. The results demonstrate both an efficient coupling of the microwave irradiation to the samples as well as an excellent sensitivity for minute changes in sample conductivity.

  PublisherOA PDFDOI

• Ultrathin Metasurface Wavelength-Selective Mirror for Millimeter/Terahertz Wave Fabry-Perot Cavities

  Journal of Infrared Millimeter and Terahertz Waves · 2020-01-23 · 5 citations

  article
  PublisherDOI

• Photodiode Response in a CH₃NH₃PbI₃/CH₃NH₃SnI₃ Heterojunction

  ACS Applied Materials & Interfaces · 2017-01-18 · 14 citations

  articleOpen access

  Here we report another surprising feature of the methylammonium metal halide material family, the phototunability of the diode response of a heterojunction made of CH3NH3PbI3 and its close relative, CH3NH3SnI3. In the dark state the device behaves as a diode, with the Sn homologue acting as the “p” side. The junction is extremely sensitive to illumination. A complete reversal of the diode polarity, the first observation of its kind, is seen when the junction is exposed to red laser light of 25 mW/cm2 or larger power density. This finding opens up the possibility for a novel class of optoelectronic devices.

  PublisherOA PDFDOI

• Metallicity and conductivity crossover in white light illuminated CH$_3$NH$_3$PbI$_3$ perovskite

  arXiv (Cornell University) · 2016-04-19 · 3 citations

  preprintOpen access

  The intrinsic d.c. electrical resistivity ($ρ$) - measurable on single crystals only - is often the quantity first revealing the properties of a given material. In the case of CH$_3$NH$_3$PbI$_3$ perovskite measuring $ρ$ under white light illumination provides insight into the coexistence of extended and shallow localized states (0.1 eV below the conduction band). The former ones dominate the electrical conduction while the latter, coming from neutral defects, serve as a long-lifetime charge carrier reservoir accessible for charge transport by thermal excitation. Remarkably, in the best crystals the electrical resistivity shows a metallic behaviour under illumination up to room temperature, giving a new dimension to the material in basic physical studies.

  PublisherOA PDFDOI

• Photodiode Response in a CH$_3$NH$_3$PbI$_3$/CH$_3$NH$_3$SnI$_3$ Heterojunction

  arXiv (Cornell University) · 2016-04-20 · 1 citations

  preprintOpen access

  Since the discovery of its photovoltaic properties organometallic salt CH$_3$NH$_3$PbI$_3$ became the subject of vivid interest. The material exhibits high light conversion efficiency, it lases in red color, and it can serve as the basis for light emitting diodes and photodetectors. Here we report another surprising feature of this material family, the photo-tunability of the diode response of a heterojunction made of CH$_3$NH$_3$PbI$_3$ and its close relative, CH$_3$NH$_3$SnI$_3$. In the dark state the device behaves as a diode, with the Sn homologue acting as the "p" side. The junction is extremely sensitive to illumination. A complete reversal of the diode polarity, the first observation of its kind, is seen when the junction is exposed to red laser light of 25 mW/cm$^2$ or larger power density. This finding opens up the possibility for a novel class of opto-electronic devices.

  PublisherOA PDFDOI

Frequent coauthors

• G. Grüner

  University of California, Los Angeles

  101 shared

• Robert L. Whetten

  Northern Arizona University

  65 shared

• O. Klein

  CEA Grenoble

  48 shared

• Richard B. Kaner

  University of California, Los Angeles

  47 shared

• François Diederich

  Central South University

  35 shared

• A. Jánossy

  31 shared

• Y. Yoshinari

  Kyoto University

  27 shared

• H. Alloul

  27 shared