THz-frequency magnon-phonon-polaritons in the collective strong-coupling regime

Abstract

We demonstrate the strong coupling of both magnons and phonons to terahertz (THz) frequency electromagnetic (EM) waves confined to a photonic crystal (PhC) cavity. Our cavity consists of a two-dimensional array of air-holes cut into a hybrid slab of ferroelectric lithium niobate (LiNbO3) and erbium orthoferrite (ErFeO3), a canted antiferromagnetic crystal. The phonons in LiNbO3 and the magnons in ErFeO3 are strongly coupled to the electric and magnetic field components of the confined EM wave, respectively. This leads to the formation of new cavity magnon-phonon-polariton modes, which we experimentally observe as a normal-mode splitting in the frequency spectrum and an avoided crossing in the temperature-frequency plot. The cavity also has a mode volume of V = 3.4 × 10 −3 λ 3 ≃ 0.5(λ/n) 3 µm 3 and can achieve a Q-factor as high as 1000. These factors facilitate the pursuit of the fields of THz cavity spintronics and quantum electrodynamics. arXiv:1707.03503v1 [physics.optics]

Manipulating quantum materials with quantum light

“…Recently, the class of available hybrid systems has been extended by solid state systems that couple strongly to microwave, terahertz or optical radiation [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. For example, the coupling of microwave cavities to magnon and spinon excitations in magnetic materials has been investigated in [12][13][14][15][16] and [17], respectively. Two-dimensional electron gases in magnetic fields can couple very strongly to terahertz cavities [18][19][20] such that Bloch-Siegert shifts become observable [21], and tomography of an ultrastrongly coupled polariton state was presented in [22] using magneto-transport measurements [23].…”

Magnon polarons in the spin Peltier effect

“…Magnetoelastic coupling (MEC), the interaction between spin waves (magnons) and lattice waves (phonons), was first investigated more than half a century ago [1][2][3] and has renewed attention in spintronics . By the MEC, magnons and phonons, in the vicinity of the crossings of their dispersion relations, are hybridized into quasiparticles called magnon polarons that share mixed magnonic and phononic characters [6,8,[10][11][12][20][21][22][23][24][25][26][27][28][29][30]. Magnon polarons can convey spin information with velocities close to those of phonons, much faster than the magnon velocities in the dipolar magnon regime [7,8,14,15].…”

Mott polaritons in cavity-coupled quantum materials

“…Collective light-matter interactions are conveniently described within the framework of polaritons, which are combined excitations of light and matter. A prominent example is given by dark-state polaritons in laserdriven atomic gases [3] and more recently, polaritons have been investigated in various solid state systems coupled to cavities [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. For example, Bose-Einstein condensation of exciton polaritons in semiconductor materials attracted considerable attention [4,5], and molecular systems [6][7][8] coupled to cavities can exhibit giant Rabi splittings between polariton branches.…”

“…For example, Bose-Einstein condensation of exciton polaritons in semiconductor materials attracted considerable attention [4,5], and molecular systems [6][7][8] coupled to cavities can exhibit giant Rabi splittings between polariton branches. The strong coupling of magnetic excitations to microwave cavities was investigated in [9][10][11][12][13][14], and two-dimensional electron gases coupled to THz cavities were studied in [15][16][17][18][19][20]. In all these systems [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], Coulomb interactions between electrons play a minor role and are not directly involved in the formation of polaritons.…”