Photoluminescence at the ground-state level anticrossing of the nitrogen-vacancy center in diamond - A comprehensive study

At a Glance

Metadata	Details
Publication Date	2021-01-20
Journal	Physical review. B./Physical review. B
Authors	Viktor Ivády, Huijie Zheng, Arne Wickenbrock, Lykourgos Bougas, Georgios Chatzidrosos
Institutions	GSI Helmholtz Centre for Heavy Ion Research, Helmholtz Institute Mainz
Citations	32
Analysis	Full AI Review Included

Technical Documentation & Analysis: Photoluminescence at the Ground State Level Anticrossing (GSLAC)

This document analyzes the research concerning the Nitrogen-Vacancy (NV) center photoluminescence (PL) at the Ground State Level Anticrossing (GSLAC) region, focusing on material requirements and applications relevant to 6CCVD’s advanced MPCVD diamond products.

Executive Summary

The research provides critical insights into optimizing NV-center-based quantum sensors and Dynamic Nuclear Polarization (DNP) systems by analyzing environmental couplings at the GSLAC (B_z ≈ 102.4 mT).

Microwave-Free Quantum Sensing: Confirms the viability of NV ensembles for microwave-free magnetometry, spectroscopy, and DNP, eliminating the need for high-power microwave driving.
Environmental Fingerprinting: Demonstrates that external fields, ¹³C nuclear spins, P1 centers, and other NV centers each produce unique, identifiable signatures in the GSLAC PL spectrum, enabling precise characterization of the diamond host material.
Isotopic Engineering Requirement: Successful application relies heavily on controlling the ¹³C isotopic abundance (ranging from natural 1.07% to highly depleted 0.01%) to manage nuclear spin bath interactions.
Defect Concentration Metrology: Establishes a novel method for measuring paramagnetic defect concentration (P1 centers) in the vicinity of NV centers, correlating P1 concentration (ppm) directly to the FWHM slope of the central PL dip (≈ 20 µT/ppm).
Advanced DNP Pathways: Proves that the NV center can directly polarize nuclear spins coupled to P1 centers, offering a new DNP mechanism that bypasses reliance on slow nuclear spin diffusion, particularly beneficial for near-surface NV applications.
¹⁵NV Potential: Highlights the superior controllability and potential of ¹⁵NV centers for magnetometry and DNP due to larger hyperfine splitting and a reduced number of state crossings compared to ¹⁴NV.

Technical Specifications

The following table summarizes the critical physical and experimental parameters extracted from the research, essential for replicating or advancing GSLAC-based quantum applications.

Parameter	Value	Unit	Context
GSLAC Magnetic Field (B_z)	±102.4	mT	Electronic ground state level anticrossing point
¹⁴NV Zero-Field Splitting (D)	2868.91	MHz	Fundamental NV property
¹⁴N Nuclear Quadrupole Splitting (Q)	-5.01	MHz	Used in Hamiltonian modeling
P1 Center Hyperfine Tensor (A_⊥^P1)	81	MHz	Transverse component
P1 Center Hyperfine Tensor (A_\|\|^P1)	114	MHz	Parallel component
¹³C Abundance (Depleted Samples)	0.01 - 0.03	%	Required for low-noise spin bath environment
NV Concentration Range Studied	0.9 ppm - 20 ppb		Range tested across samples IS, E6, W4
P1 Concentration Range Studied	1 - 200	ppm	Used to study defect coupling and broadening
Theoretical FWHM Gradient (¹⁴NV)	3.36	mTmT^-1	Dependence on external transverse field
P1 Concentration FWHM Slope	≈ 20	µT/ppm	Used for defect concentration measurement
Simulation Ground State Dwell Time (t_GS)	3	µs	Coherent evolution period during optical cycling
Simulation Optical Pumping Rate	333	kHz	Used for DNP simulations

Key Methodologies

The study utilized a combination of advanced experimental techniques and theoretical modeling to characterize the NV-environment interactions at the GSLAC.

Sample Preparation: Utilized four distinct diamond samples (W4, IS, E6, F11) varying widely in NV concentration (ppb to ppm), P1 concentration (ppm), and ¹³C isotopic abundance (natural 1.07% down to 0.01% depleted).
Photoluminescence (PL) Measurement: PL spectra were recorded using a custom-built experimental apparatus featuring a computer-controlled 3-D translation stage, rotation stage, and an electromagnet capable of generating fields up to 110 mT.
Theoretical Modeling (External Fields): The density matrix ($\rho$) of a single NV center was propagated using the master equation of a closed system over a 0.1 ms interval to calculate average PL intensity, allowing for the simulation of minuscule PL features induced by weak transverse magnetic fields.
Theoretical Modeling (Environmental Spins): The extended Lindblad formalism was applied to simulate spin-relaxation effects from environmental spins (¹³C, P1, other NV centers). This involved modeling the system as a central NV center surrounded by a randomly distributed spin bath.
Dynamic Nuclear Polarization (DNP) Simulation: For the ¹³C spin bath, simulations included a sequence of optical excitation cycles (3 µs dwell time) and spin-selective optical excited processes to model continuous optical pumping and nuclear spin polarization transfer.
Coupling Tensor Calculation: Hyperfine coupling tensors (for ¹³C) were determined via first principles Density Function Theory (DFT) calculations, while coupling tensors for P1 and NV spin baths were calculated using the dipole-dipole interaction Hamiltonian.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials required to replicate, extend, and commercialize the microwave-free quantum sensing and DNP applications detailed in this research. Our ability to control isotopic purity, defect concentration, and surface finish ensures optimal performance for GSLAC-based devices.

Applicable Materials

To achieve the precise spin bath engineering demonstrated in the paper, 6CCVD recommends the following materials:

Application Focus	6CCVD Material Recommendation	Key Specification
High-Resolution Sensing / Low Noise	Isotopically Pure SCD (Single Crystal Diamond)	¹²C enrichment < 0.03% (matching Sample E6/IS purity) to minimize ¹³C spin bath decoherence.
High-Density DNP / Ensemble Sensing	Engineered PCD (Polycrystalline Diamond)	Plates up to 125mm diameter with controlled NV concentration (0.5 ppm to 5 ppm) for high signal-to-noise ratio.
¹⁵NV Research	Custom ¹⁵N Doped SCD	SCD grown using ¹⁵N precursors to leverage the superior controllability and reduced state crossings of the ¹⁵NV center.
Defect Metrology Calibration	SCD with Controlled P1/NV Ratio	SCD wafers with precisely engineered, known concentrations of P1 centers (1 ppm to 200 ppm) for calibrating GSLAC PL defect measurement tools.

Customization Potential

The success of GSLAC applications hinges on precise material engineering, which is 6CCVD’s core expertise:

Isotopic Control: We offer diamond substrates with custom ¹³C isotopic depletion (< 0.01%) or enrichment, essential for tuning the nuclear spin bath environment and maximizing coherence time.
Defect Engineering: NV and P1 concentrations can be custom-tuned during MPCVD growth from the ppb range (for isolated NV studies) up to the ppm range (for high-sensitivity ensemble sensing).
Dimensional Flexibility: We provide custom plates and wafers up to 125mm (PCD) and SCD wafers up to 500 µm thick, allowing for scalable device fabrication.
Surface Preparation: For near-surface NV applications critical for DNP transfer to external media, we guarantee ultra-low roughness polishing (Ra < 1 nm for SCD) to maintain NV integrity and minimize surface noise.
Metalization Services: Although not the primary focus of this paper, 6CCVD offers in-house custom metalization (Au, Pt, Ti, W, Cu) for integrating electrodes or contacts onto diamond substrates for advanced device architectures.

Engineering Support

6CCVD’s in-house PhD team specializes in the physics of color centers and spin dynamics. We provide comprehensive engineering support to assist researchers in:

Material Selection: Guiding the choice between SCD and PCD, and determining optimal ¹³C depletion levels based on target coherence times and operating temperatures.
Defect Recipe Optimization: Developing custom MPCVD growth recipes to achieve the precise NV and P1 concentrations required for microwave-free DNP and magnetometry projects.
Advanced Characterization: Assisting with the interpretation of material properties relevant to GSLAC PL signatures, ensuring the supplied diamond meets the stringent requirements for quantum applications.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

The nitrogen-vacancy center (NV center) in diamond at magnetic fields\ncorresponding to the ground state level anticrossing (GSLAC) region gives rise\nto rich photoluminescence (PL) signals due to the vanishing energy gap between\nthe electron spin states, which enables to have an effect on the NV center’s\nluminescence for a broad variety of environmental couplings. In this article we\nreport on the GSLAC photoluminescence signature of NV ensembles in different\nspin environments at various external fields. We investigate the effects of\ntransverse electric and magnetic fields, P1 centers, NV centers, and the\n$^{13}$C nuclear spins, each of which gives rise to a unique PL signature at\nthe GSLAC. The comprehensive analysis of the couplings and related optical\nsignal at the GSLAC provides a solid ground for advancing various\nmicrowave-free applications at the GSLAC, including but not limited to\nmagnetometry, spectroscopy, dynamic nuclear polarization (DNP), and nuclear\nmagnetic resonance (NMR) detection. We demonstrate that not only the most\nabundant $^{14}$NV center but the $^{15}$NV can also be utilized in such\napplications and that nuclear spins coupled to P1 centers can be polarized\ndirectly by the NV center at the GSLAC, through a giant effective nuclear\n$g$-factor arising from the NV center-P1 center-nuclear spin coupling. We\nreport on new alternative for measuring defect concentration in the vicinity of\nNV centers and on the optical signatures of interacting, mutually aligned NV\ncenters.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevb.103.035307