Thermodynamic Phase Diagram of Static Charge Order in Underdoped YBa₂Cu₃O₆₊y
The paper of high-temperature superconductivity in cuprate materials, particularly in compounds like YBa₂Cu₃O₆₊y (YBCO), has necessitated an intricate examination of the interaction between superconductivity and competing charge orders. This paper investigates the elusive thermodynamic phase transition associated with charge ordering in underdoped YBCO and elaborates on the dimensionality of the charge modulations. Utilizing sound velocity measurements in high magnetic fields, the authors provide a significant contribution to understanding the complex phase diagram of YBCO, specifically focusing on the static charge order induced by magnetic fields.
Through precise measurement of sound velocities across various acoustic modes, this research identifies a thermodynamic signature of the field-induced charge ordering phase transition. By constructing a detailed field-temperature phase diagram, this paper reveals the competitive nature of charge ordering against superconductivity. The transition to static charge order is identified at approximately 18 T, with a nearly constant onset temperature below 40 K. This contrasts with the melting transition of the vortex lattice, which occurs at a lower field and exhibits different temperature dependence.
The paper explores the analysis of charge modulation symmetry using group theory, backed by elastic constant anomalies in various acoustic modes. Evidence supports a two-dimensional character of the charge modulation, with significant implications for the topology of the reconstructed Fermi surface. This finding imposes constraints that favor scenarios where static charge ordering at low temperatures arises from freezing charge fluctuations observed at high temperatures, rather than unidirectional modulation.
Experimental techniques used to establish these observations include high precision ultrasonic sound velocity measurements, performed across a range of magnetic fields up to 60 T. These measurements reveal dual phase transitions at the charge order (B_co) and vortex lattice melting (B_m), indicating the distinct nature of charge ordering transition independent from vortex dynamics. Notably, the dimensionality assessment suggests a biaxial modulation rather than alternating domains of uniaxial CDWs, refining current models of charge density distribution in cuprates.
The implications of these findings are profound, offering insights into the phase diagram of cuprate superconductors. The templates established by these measurements shape theoretical expectations of how competing orders—charge orders and superconductivity—interact within YBCO and potentially other cuprate systems, strengthening the link between orthorhombic structural considerations and electronic transport properties. Future developments in this area could refine models of superconductivity and enhance the design of materials that exploit these complex interactions to achieve desired electronic characteristics.
This paper improves our understanding of how magnetic fields influence charge order transitions and sheds light on the subtle interplay between different phases in high-temperature superconductors. Further inquiries into similar systems could pave the way for more efficient strategies to manipulate superconducting properties, thereby contributing valuable knowledge toward innovative applications in electronic and magnetic devices.
