Magnetic metamaterials composed of split-ring resonators or U-type elements may exhibit discreteness effects in THz and optical frequencies due to weak coupling. We consider a model one-dimensional metamaterial formed by a discrete array of nonlinear split-ring resonators where each ring interacts with its nearest neighbors. On-site nonlinearity and weak coupling among the individual array elements result in the appearance of discrete breather excitations or intrinsic localized modes, both in the energy-conserved and the dissipative system. We analyze discrete single and multibreather excitations, as well as a special breather configuration forming a magnetization domain wall and investigate their mobility and the magnetic properties their presence induces in the system.

We introduce a one dimensional parity-time (PT )-symmetric nonlinear magnetic metamaterial consisting of split-ring dimers having both gain and loss. When nonlinearity is absent we find a transition between an exact to a broken PT -phase; in the former the system features a two band gapped spectrum with shape determined by the gain and loss coefficients as well as the inter-unit coupling. In the presence of nonlinearity we show numerically that as a result of the gain/dissipation matching a novel type of long-lived stable discrete breathers can form below the lower branch of the band with no attenuation. In these localized modes the energy is almost equally partitioned between two adjacent split rings on the one with gain and the other one with loss.PACS numbers: 63.20. Pw, 11.30.Er, 78.67.Pt Considerable research effort has recently focused in the investigation and developement of artificial materials that exhibit properties not found in nature. In the electromagnetic domain, these advances resulted in the construction of metamaterials, novel artificial structures that provide full access to all four quadrants of the real permittivity -permeability plane [1]. Recently, there has been increasing interest in synthetic materials with a combined parity -time (PT ) symmetry. Although quantum systems described by PT −symmetric Hamiltonians have been studied for many years ([2] and refs. therein), it was only recently realized that many classical systems are PT −symmetric [3]. Subsequently, the notion of PT symmetry has been extended to dynamical lattices, particularly in optics [4,5]. Soon after that, PT −symmetry breaking was experimentally observed [6][7][8]. Such considerations have been also extended in nonlinear lattices, where the existence of stable discrete solitons [9] and Talbot effects [10] was theoretically demonstrated.Among recent developements in PT −symmetric materials, the application of these ideas in electronic circuits [11] not only provides a platform for testing the new ideas within the framework of easily accessible experimental configurations, but also provides a link to metamaterials. Conventional, metallic metamaterials suffer from high losses that hamper their use in practical applications. However, building metamaterials with PT symmetry, relying on gain and loss, may provide a way out and moreover lead to new extraordinary properties. It is shown that PT −symmetric metamaterials undergo spontaneous symmetry breaking from the exact PT phase (real eigenfrequencies) to the broken PT phase (at least a pair of complex eigenfrequencies), with variation of the gain/loss coefficient. In the presence of nonlinearity, the generation of long-lived excitations in the form of discrete breathers (DBs) [12] is demonstrated numerically in metamaterial models. These novel gain-driven DBs, generated either by proper intialization of the PT metamaterial or purely dynamically through external driving, result from power matching of the input power through the gain mechanism and internal loss.SRR with Loss ...