USC USC Takahashi Group


Supported by

Anton B. Burg Foundation

Zumberge Research Fund

Contact information

Department of Chemistry
840 Downey Way
University of Southern California
Los Angeles, CA 90089-0744

Last modified: 09/12/2015

Takahashi research group

Welcome to the Takahashi Lab at USC.

We are an interdisciplinary experimental research group overlapping in the areas of Condensed Matter Physics, Chemical Physics and Biophysics.

Our current research interests include,
- Spin dynamics of a single nitrogen-vacancy (NV) center in diamond,
- Development of single-molecule magnetic resonance techniques using a NV,
- Nanomagnetism in quantum molecular magnets,
- Conformational dynamics in biological systems.

Group photo at Griffith Park


Understanding the Linewidth of the ESR Spectrum Detected by a Single NV Center in Diamond

Prep B. Fortman and S. Takahashi
J. Phys. Chem. A 123, 6350-6355 (2019)

Spectral analysis of electron spin resonance (ESR) is a powerful technique for various investigations including characterization of spin systems, measurements of spin concentration, and probing spin dynamics. The nitrogen-vacancy (NV) center in diamond is a promising magnetic sensor enabling improvement of ESR sensitivity to the level of a single spin. Therefore, understanding the nature of NV-detected ESR (NV-ESR) spectrum is critical for applications to nanoscale ESR. Within this work we investigate the linewidth of NV-ESR from single substitutional nitrogen centers (called P1 centers). NV-ESR is detected by a double electron-electron resonance (DEER) technique. By studying the dependence of the DEER excitation bandwidth on NV-ESR linewidth, we find that the spectral resolution is improved significantly and eventually limited by inhomogeneous broadening of the detected P1 ESR. Moreover, we show that the NV-ESR linewidth can be as narrow as 0.3 MHz. (read more...)

Investigation of Near-Surface Defects of Nanodiamonds by High-Frequency EPR and DFT Calculation

Prep Z. Peng, T. Biktagirov, F. H. Cho, U. Gerstmann and S. Takahashi
J. Chem. Phys. 150 , 134702 (2019)

Nanodiamonds (NDs) hosting nitrogen-vacancy (NV) centers are a promising platform for quantum sensing applications. Sensitivity of the applications using NV centers in NDs is often limited due to the presence of paramagnetic impurity contents near the ND surface. Here, we investigate near-surface paramagnetic impurities in NDs. Using high-frequency (HF) electron paramagnetic resonance spectroscopy, the near-surface paramagnetic impurity within the shell of NDs is probed and its g-value is determined to be 2.0028(3). Furthermore, HF electron-electron double resonance-detected nuclear magnetic resonance spectroscopy and a first principles calculation show that a possible structure of the near-surface impurity is the negatively charged vacancy V?. The identification of the near-surface impurity by the present investigation provides a promising pathway to improve the NV properties in NDs and the NV-based sensing techniques. (read more...)

Determination of nitrogen spin concentration in diamond using double electron-electron resonance

Prep V. Stepanov and S. Takahashi
Phys. Rev. B 94 , 024421 (2016)

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. (read more...)

Investigating functional DNA grafted on nanodiamond surface using site-directed spin labeling and electron paramagnetic resonance spectroscopy

Prep R. D. Akiel, X. Zhang, C. Abeywardana, V. Stepanov, P. Z. Qin and S. Takahashi
J. Phys. Chem. B 120 , 4003 (2016)

Nanodiamonds (NDs) are a new and attractive class of materials for sensing and delivery in biological systems. Methods for functionalizing ND surfaces are highly valuable in these applications, yet reported approaches for covalent modification with biological macromolecules are still limited, and characterizing behaviors of ND-tethered biomolecules is difficult. Here we demonstrated the use of copper-free click chemistry to covalently attach DNA strands at ND surfaces. Using site-directed spin labeling and electron paramagnetic resonance spectroscopy, we demonstrated that the tethered DNA strands maintain the ability to undergo repetitive hybridizations and behave similarly to those in solutions, maintaining a large degree of mobility with respect to the ND. The work established a method to prepare and characterize an easily addressable identity tag for NDs. This will open up future applications such as targeted ND delivery and developing sensors for investigating biomolecules. (read more...)

Spin coherence in a Mn3 single-molecule magnet

Prep C. Abeywardana, A. M. Mowson, G. Christou, and S. Takahashi
Appl. Phys. Lett. 108 , 042401 (2016)

Spin coherence in single crystals of the spin S?=?6 single-molecule magnet (SMM) [Mn3O(O2CEt)3(mpko)3]+ (abbreviated Mn3) has been investigated using 230?GHz electron paramagnetic resonance spectroscopy.Coherence in Mn3 was uncovered by significantly suppressing dipolar contribution to the decoherence with complete spin polarization of Mn3 SMMs. The temperature dependence of spin decoherence time (T2) revealed that the dipolar decoherence is the dominant source of decoherence in Mn3 and T2 can be extended up to 267?ns by quenching the dipolar decoherence. (read more...)

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

Prep V. Stepanov, F. H. Cho, C. Abeywardana and S. Takahashi
Appl. Phys. Lett. 106 , 063111 (2015)

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 (T1) of NV centers in nanodiamonds. (read more...)