Studying critical parameters of superconductor via diamond quantum sensors
Kin On Ho, Wai Kuen Leung, Yiu Yung Pang, King Yau Yip, Jianyu Xie, Yiran Liu, Aliki Sofia Rotelli, Man Yin Leung, Ho Yin Chow, Kwing To Lai, Andrej Denisenko, B. Keimer, Jörg Wrachtrup, Sen Yang
Abstract Critical parameters are the key to superconductivity research, and reliable instrumentations can facilitate the study. Traditionally, one has to use several different measurement techniques to measure critical parameters separately. In this work, we develop the use of a single species of quantum sensor to determine and estimate several critical parameters with the help of independent simulation data. We utilize the nitrogen-vacancy (NV) center in the diamond, which recently emerged as a promising candidate for probing exotic features in condensed matter physics. The non-invasive and highly stable nature provides extraordinary opportunities to solve scientific problems in various systems. Using a high-quality single-crystalline YBa2Cu4O8 (YBCO) as a platform, we demonstrate the use of diamond particles and a bulk diamond to probe the Meissner effect. The evolution of the vector magnetic field, the H − T phase diagram, and the map of fluorescence contour are studied via NV sensing. Our results reveal different critical parameters, including lower critical field H c 1 , upper critical field H c 2 , and critical current density j c , as well as verifying the unconventional nature of this high-temperature superconductor YBCO. Therefore, NV-based quantum sensing techniques have huge potential in condensed matter research.
Abstract Critical parameters are the key to superconductivity research, and reliable instrumentations can facilitate the study. Traditionally, one has to use several different measurement techniques to measure critical parameters separately. In this work, we develop the use of a single species of quantum sensor to determine and estimate several critical parameters with the help of independent simulation data. We utilize the nitrogen-vacancy (NV) center in the diamond, which recently emerged as a promising candidate for probing exotic features in condensed matter physics. The non-invasive and highly stable nature provides extraordinary opportunities to solve scientific problems in various systems. Using a high-quality single-crystalline YBa2Cu4O8 (YBCO) as a platform, we demonstrate the use of diamond particles and a bulk diamond to probe the Meissner effect. The evolution of the vector magnetic field, the H − T phase diagram, and the map of fluorescence contour are studied via NV sensing. Our results reveal different critical parameters, including lower critical field H c 1 , upper critical field H c 2 , and critical current density j c , as well as verifying the unconventional nature of this high-temperature superconductor YBCO. Therefore, NV-based quantum sensing techniques have huge potential in condensed matter research.
Single qubit in solid-state materials recently emerges as a versatile platform for quantum information. Among them, the nitrogen vacancy (NV) centre in diamond has become a powerful tool in quantum sensing for detecting various physics parameters, including electric and magnetic fields, temperature, force, strain, with ultimate precision and resolutions. It has been widely used in different conditions, from samples in ambient to samples in ultra-high pressure and low temperature. It can detect quantum phase transitions as well as neuron activities. Here we give a general review on both the physics of the sensing mechanism and protocols and applications.
In modern-day quantum metrology, quantum sensors are widely employed to detect weak magnetic fields or nanoscale signals. Quantum devices, exploiting quantum coherence, are inevitably connected to physical constants and can achieve accuracy, repeatability, and precision approaching fundamental limits. As a result, these sensors have shown utility in a wide range of research domains spanning both science and technology. A rapidly emerging quantum sensing platform employs atomic-scale defects in crystals. In particular, magnetometry using nitrogen-vacancy (NV) color centers in diamond has garnered increasing interest. NV systems possess a combination of remarkable properties, optical addressability, long coherence times, and biocompatibility. Sensors based on NV centers excel in spatial resolution and magnetic sensitivity. These diamond-based sensors promise comparable combination of high spatial resolution and magnetic sensitivity without cryogenic operation. The above properties of NV magnetometers promise increasingly integrated quantum measurement technology, as a result, they have been extensively developed with various protocols and find use in numerous applications spanning materials characterization, nuclear magnetic resonance (NMR), condensed matter physics, paleomagnetism, neuroscience and living systems biology, and industrial vector magnetometry. In this chapter, NV centers are explored for magnetic sensing in a number of contexts. In general, we introduce novel regimes for magnetic-field probes with NV ensembles. Specifically, NV centers are developed for sensitive magnetometers for applications where microwaves (MWs) are prohibitively invasive and operations need to be carried out under zero ambient magnetic field. The primary goal of our discussion is to improve the utility of these NV center-based magnetometers.
Microscopic studies on thin film superconductors play an important role for probing non-equilibrium phase transitions and revealing dynamics at the nanoscale. However, magnetic sensors with nanometer scale spatial and picosecond temporal resolution are essential for exploring these. Here, we present an all-optical, microwave-free method that utilizes the negatively charged nitrogen-vacancy (NV) center in diamond as a non-invasive quantum sensor and enables the spatial detection of the Meissner state in a superconducting thin film. We place an NV implanted diamond membrane on a 20nm thick superconducting La2−xSrxCuO4 (LSCO) thin film with Tc of 34K. The strong B-field dependence of the NV photoluminescence allows us to investigate the Meissner screening in LSCO under an externally applied magnetic field of 4.2mT in a non-resonant manner. The magnetic field profile along the LSCO thin film can be reproduced using Brandt’s analytical model, revealing a critical current density jc of 1.4×108A/cm2. Our work can be potentially extended further with a combination of optical pump probe spectroscopy for the local detection of time-resolved dynamical phenomena in nanomagnetic materials.
Recently, superconductivity under high pressure in hydrogen-rich compounds, such as H3S (Tc=203K at 150 GPa) and LaH10 (Tc=253K at 200 GPa), has attracted extensive research interest due to their high superconducting transition temperatures (Tc). However, magnetic measurements of these materials are significantly challenging in terms of sensitivity and spatial resolution. Consequently, magnetometry under high pressure using nitrogen-vacancy (NV) centers has recently begun to be implemented. The NV center is a promising sensor and is expected to overcome this problem because of its properties, including its size and measurement principles. In this article, we conducted wide-field magnetic imaging using NV centers at low temperatures and pressures of several GPa. The details of the developed measurement system and its application to a cuprate superconductor are demonstrated. By employing our method, the visualization of the Meissner effect in hydride superconductors is anticipated.
Extreme conditions, such as ultra-low temperatures, high pressures, and strong magnetic fields, are critical to producing and studying exotic states of matter. To measure physical properties under extreme conditions, the advanced sensing schemes are required. As a promising quantum sensor, the diamond nitrogen-vacancy (NV) center can detect magnetic field, electronic field, pressure, and temperature with high sensitivity. Considering its nanoscale spatial resolution and ultra-wide working range, the diamond quantum sensing can play an important role in frontier studies involving extreme conditions. This paper reviews the spin and optical properties of diamond NV center under extreme conditions, including low temperature, high temperature, zero field, strong magnetic fields, and high pressures. The opportunities and challenges of diamond quantum sensing under extreme conditions are discussed. The basic knowledge of spin-based quantum sensing and its applications under extreme conditions are also covered.
The spatial distribution of a magnetic field can be determined with micrometer resolution using widefield nitrogen vacancy (NV) center magnetic imaging. Nevertheless, reconstructing the magnetic field from the raw data can be challenging due to the degeneracy of the four possible NV axes and the tremendous amount of data. While a qualitative approach is sufficient for most analyses, a quantitative analysis offers deeper insight into the physical system. Here, we apply NV widefield magnetic imaging to a HgBa2Ca2Cu3O8+δ (Hg-1223) superconducting microcrystal at a pressure of 4 GPa. We fit the results with solutions from the Hamiltonian describing the NV center ground state and take into account the relative intensities of the resonances to determine the local magnetic field magnitude and angle. Thus, we reconstruct the temperature-dependent expulsion of the magnetic field due to the Meissner effect around the superconductor. By comparing the resulting parameters to Brandt's model, which describes the magnetic behavior of a type-II superconductor, we extract the critical current density jc. Overall, this work showcases the first widefield quantitative reconstruction of the Meissner effect under pressure and an optical method to study critical current density. Thus, it provides new insights into the application of NV magnetometry to superconductivity research at high pressures.